|
The Next DNA Forensics Challenge
By Ko Endo and Randy Nagy
The increased use of DNA analysis in forensic investigations, the expansion
of the FBI CODIS (Combined DNA Indexing System) database and the automation
of newer DNA analysis technologies have greatly increased the amount of DNA
data being generated in crime laboratories today. The management and integration
of all this new data is becoming increasingly complex and challenging.
The high level of discrimination offered by DNA analysis technology, the faster
processing of samples and the comfort level of prosecutors working cases with
DNA analyzed evidence has greatly increase the demand for DNA analysis. Many
states have expanded legislation so that over half of them require the collection
of a DNA sample from someone charged with any type of felony. Some states require
DNA collection from individuals arrested with certain types of crimes. The DNA
samples collected need to be analyzed, the data reviewed and the results uploaded
into the FBI’s CODIS database. Many crime laboratories cannot handle the tens
of thousands of samples added to their workload when new legislation passes
and existing data management systems do not allow for maximum use of the data
once it has been entered into state databases.
Meeting this challenge with information technology can improve laboratory efficiency
and reduce errors in analysis. Managing the increased volume of DNA samples
collected, processing the data efficiently and integrating this data with other
databases of criminal history requires significant resources and technological
expertise. Additionally, the data must have the highest accuracy to ensure usefulness
of the data due to the high discriminatory level of DNA. It is important that
information infrastructure support with technical personnel be included in expansion
plans of DNA analysis capabilities, otherwise the technical staff will spend
inordinate amounts of time with paper log sheets, work sheets, analysis, case
report writing, collating and filing, which takes away from precious laboratory
time.
Development and implementation of an integrated data management solution is
critical to assist with the enormous amount of new data being generated. From
the moment of evidence and data collection through the process of generating
DNA profiles, court testimonies and DNA case dispositions, all phases of the
forensics process must be considered. Through automation and strategic use of
information technology, sample integrity and productivity can be enhanced.
Portable Data Collection Device
From the beginning of the collection of samples at crime scenes, mass-casualty
disasters or convicted offender samples, the proper inventorying and logging
is a key to an efficient and effective chain of custody. For example, an automated
portable collection data collection system will minimize transcriptions of information
throughout the process and begin the electronic evidentiary chain of custody
process. Extensive use of bar codes for logging samples will eliminate transcription
errors. A more uniform and standardized method can be instituted by using an
electronic format. It is possible to build database applications on handheld
platforms that a crime scene investigator can record and catalog samples and
may dock or wirelessly transmit a list of the evidence to begin the accessioning
process within the laboratory information system.
Bode Technology Group has developed a highly portable data collection device
consisting of a special version of a popular PDA integrated with a barcode scanner
that is designed to work in challenging environments. Not only is this type
of PC very unobtrusive and mobile, it is a low cost solution that transmits
or transfers the sample collection data to the DNA laboratory information management
system. This would occur as a seamless electronic hand-off of a manifest for
the samples that are coming into the laboratory. This feature is useful for
case workload planning and assignments for laboratory directors.
An evidence-sample reconciliation module would assure forensic compliance requirements
and tracking the samples throughout the analytic process. Any discrepancies
noted can be easily recognized and tracked. The conditions of samples, transportation
method, when the sample was received and number of samples should all be noted.
An individual responsible for the receipt of the case should assure all of these
issues are resolved prior to beginning any testing procedure.
Laboratory Information System
The laboratory information management system (LIMS) is the core of an integrated
data management system. LIMS generally uses a centralized database and an application
program which provides a user interface to maintain such items as sample status,
serves as an oversight for chain of custody, and turnaround times. Once samples
have been received at a laboratory, the samples must be tracked throughout the
analysis process. It is important that all information associated with a case
be tracked and captured.
Configured with advanced login methods, a bar coded identification card, SmartCard
or a biometric such as a fingerprint can be employed to assure security and
proper assignment to cases. A database table of laboratory personnel can maintain
training status, proficiency and competency testing, employee number and other
kinds of data.
In the laboratory, instruments can be coded and tracked for trend analysis,
case history information, workload recording, and preventive maintenance records.
Also reagents, dilution figures, quality control samples and ladders that may
have lot numbers, expiration dates can be maintained. If the database application
can be programmed with context sensitive menus that direct testing personnel
with the correct reagents, reaction volumes, dilution ratios, controls and so
forth, this should minimize the possibility of errors during analysis. All of
the information will be associated and tracked with the particular sample, or
case number for later reporting.
A feature that may be considered when designing or deploying a LIMS is the
ability to manage the DNA analysis process with different amplification methods
and platforms. Although methods change, there are fundamental data fields that
will always be required for legal purposes. Therefore, as long as primary required
data fields can be identified, additional features using new data fields can
be incorporated in the future.
If you are working with a number of physically separated laboratories, an enterprise
solution should be considered to be able to develop and administer databases
centrally. In this way, all laboratories can follow one standard and share a
common database. When designing an enterprise system, make certain you receive
input from all parties involved and all features desired and required should
be carefully thought out before one line of code is written. During planning
and design phase of a LIMS, enlisting the aid of information technology personnel
to serve as a liaison between the laboratory and developers is essential. This
process of requirements collection is the most important aspect of the development
of a LIMS whether it is a completely custom application or an off the shelf
product. An outside consultant or a project manager with knowledge and experience
in both disciplines would be able to package the project to meet the needs of
both the client and developers.
Identity Verification and Authentication
A large challenge for laboratories is the positive verification and identification
of the individual associated with a biometric sample. The value of a biometric
profile, such as fingerprints or DNA sample is directly tied to the assurance
that it is the correct individual. For instance, during the collection of reference
samples from suspects, the incorrect association of demographic information
to a sample can result in duplicate testing, aliases and confusion in cases.
In some laboratories, the number of repeat offenders in the DNA databanking
projects causes multiple testing, manual checking of fingerprints, and uncertainty
of their ability to manage aliases.
One method of verifying identity is the use of public records in an iterative
questioning process. An identification card or some paper form of identity has
too much potential for forgeries and fraud. At this time, fingerprints are the
most effective and powerful biometric tool to identify an individual, provided
they are in an accessible database. In a closed demographic group such as convicted
felons, fingerprints should be used where possible to identify individuals for
sample collections. A rapid, real-time system that checks fingerprints can enhance
the identification and verification process. We have developed a solution to
collect a single fingerprint such as an index finger and search a fingerprint
database to verify the individual. The information stored can bring up photos
from identification cards and other information.
DNA Data Review Software
Finally, with the numbers of DNA profiles generated increasing so rapidly,
laboratories need to significantly increase their capacity to analyze samples
and technical review data before unloading into CODIS. Many laboratories have
turned to outside help in performing the laboratory work; however, the laboratory
still faces the daunting task of reviewing and assuring that the data is correct
and must certify them. For some laboratories, this review process is also outsourced.
The current workload of cases takes precedent over data banking samples for
CODIS and analysts cannot devote time to the project. Many government laboratories
also face funding shortages to hire more analysts. An electronic review application
can assist analysts to rapidly review data and assure that well-established
acceptance and criteria for casework or databanking are met. The software would
filter the results using thresholds defined by the CODIS administrator. The
software confirms data that meets the defined thresholds but flags samples of
interest or samples requiring human intervention and interpretation. In this
manner, improved accuracy and productivity can be expected by prescreening samples
to determine how the results meet the established thresholds. Laboratories can
improve the efficiency of the data review process, thereby increasing upload
speed of data into CODIS.
When samples and results are managed in an electronic manner, the forensic
laboratory will be able to achieve a greater level of productivity, accuracy
and compliance. As we face the challenges of more inclusive legislation and
higher demands for DNA testing, electronic data management will become more
and more crucial to the forensic laboratory. Today’s forensic laboratory director
has more decisions and choices regarding the solutions but must critically evaluate
each of them to apply technology to the highest return on investment. Shrinking
budgets and resources will force all of us to look towards a more reliable and
efficient system to handle the processing of samples. Each of the samples in
our evidence property rooms has victims behind it awaiting analysis and justice
to be served.
Ko Endo and Randy Nagy are with Bode Technology Group, a ChoicePoint company.
CASE STUDY#1
DNA Collection Made Easy: A Case Study With the Michigan State Police
By Betsy Moran, PhD
The use of DNA in criminal investigations is truly ingenious, but it is also
expensive. States across the country struggle with the time and costs associated
with collecting DNA samples to enter into the FBI’s Combined DNA Index System
(CODIS), a national computerized database that consists of DNA profiles from
convicted offenders that can be cross checked to investigate crimes. Michigan
is no exception. In 2000, it passed a law requiring that samples be taken from
all convicted felons and DNA profiles entered into the CODIS database. In 2002,
law enforcement personnel solved more than 10 “cold cases,” those more than
20 years old. For example, the murder of an elderly Texas woman in 1994 was
traced to Rodrigo Hernandez, a 29-yearold paroled inmate from the Michigan Department
of Corrections. Hernandez’ DNA sample was submitted to the Michigan State Forensic
Laboratory in Lansing. Following analysis, the DNA profile was entered into
the national CODIS database, where it matched evidence in the murder case in
Texas. The authorities in Texas were not originally aware Hernandez was in Texas
at the time of the murder and therefore did not consider him a suspect. Based
on the DNA evidence, extradition proceedings began to try Hernandez for murder
in Texas.
Information shared between law enforcement agencies highlights the promise
of DNA profiling applications and the power of CODIS. However, the process of
integrating this DNA technology into crime labs and entering all the profiles
into CODIS will take years. Because of the enormous backlog of uncollected DNA
samples from convicted felons in the Michigan system, the state police moved
from collecting blood samples, which required specially trained personnel, to
buccal samples. Today, buccal samples need to be taken from 50,000 felons incarcerated
in Michigan prisons, with new crimes taking priority.
Crime labs are currently improving their processes and infrastructure to increase
their sample throughput. The costs of DNA handling equipment, supplies, training
and further education as well as modifications to space to accommodate equipment
contribute to slow sample processing. In addition, many crime labs outsource
DNA analysis to address backlog or program implementation issues.
Collecting and processing DNA for inclusion into a database is a complicated
and time-consuming procedure. Forensic labs develop DNA profiles from blood
and/or buccal samples of convicted criminals that were taken upon conviction
or collected from incarcerated felons. The labs also work up genetic profiles
from biological evidence left behind at crime scenes, such as blood, semen,
skin, saliva or perspiration.
Once collected, DNA profiles are coded into two separate index files, a local
file and a federal file. Then the CODIS software program searches both indexes
for matching profiles. The searches can be done locally, between states and
nationally, so investigators can link DNA from the scenes of unsolved crimes
to the “genetic fingerprint” of convicted criminals in the database. Early methods
of sample collection and analysis technologies were complex and tedious. Further,
freezer space for storage of samples is limited and expensive, and all it takes
is a single power outage to destroy irreplaceable DNA specimens.
Whatman FTA is making the buccal sample collection, purification and DNA preservation
process more straightforward with its revolutionary filter technology. Sampling
is made easier as swabs containing buccal cells are simply pressed onto Whatman
FTA cards. A dye indicator incorporated into the FTA card turns from pink to
white after the sample is applied to indicate the location of the sample.
Typical DNA collection using blood drawn into tubes by a specially trained
staff and a controlled climate to store samples increases the cost of shipping
DNA samples to the lab for evaluation. FTA is a convenient, cost effective alternative.
Whatman FTA provides a proven solution that allows police to easily collect
samples and store them reliably at room temperature for years without the risk
of sample degradation. To date, DNA has been stored at room temperature on FTA
for more than 14 years. Alternatively, crime labs have the option to prepare
DNA for analysis directly on FTA in less than 30 minutes without the need for
an expensive kit.
During collection of samples for DNA analysis, the police are exposed to potentially
infectious pathogens. The Michigan State Police were interested in FTA because
it not only stabilizes the DNA needed for analysis but also inactivates pathogens,
making the samples safe for handling by laboratory personnel. According to Charles
Barna, CODIS state administrator for the Michigan State Police, “Convenience
and stability — those are the reasons we’ve continued to use it. FTA renders
the sample extremely safe. These are important issues when you are putting biology
collection in the hands of general law enforcement.”
More than 600 law enforcement individuals are using Whatman FTA to collect
samples. “The big advantage is that you can train law enforcement personnel,
people unfamiliar with laboratories and DNA to do this in many environments.
It is important to have success the first goround in sample collection,” Barna
adds. “You don’t want to have to go back and do it two or three times. A lot
of people we are collecting from are not easily accessible.”
The Michigan State Police validated the Whatman FTA approach and have been
using it to maintain blood and buccal samples ever since it was introduced to
the market.
The police forensic scientists heard about the virtues of FTA’s effectiveness
from scientific meetings and user networking.
“Because we had already validated FTA, we decided that it was an extension
of technology that fits what we need today,” Barna says. “With Whatman FTA technology,
Michigan State Police have been able to dramatically increase lab throughput,
proving the product to be one of the most efficient methods to collect, transport,
achieve and purify DNA.”
Betsy Moran, PhD, is technical marketing manager of genetic ID markets at
Whatman, based in Clifton, N.J.
CASE STUDY#2
Processing Large Numbers of Samples from a Mass Fatality:
What the Work Identifying Victims of the World Trade Center Has Taught
the Forensic Community
By Kevin C. McElfresh, PhD and Mitchell Holland, PhD
DNA analysis has played a significant role in human remains identification
for mass fatality incidents in the United States since the TWA Flight 800 commercial
airliner crash in 1996.
In the past seven years, DNA analysis has played a role in identifying victims
in other commercial airline crashes, including Korean Air Flight 801 in 1997,
Egypt Air Flight 990 in 1999, Alaska Airlines Flight 261 in 2000, and American
Airlines Flight 587 in 2001 (See www.ntsb.gov).
The majority of the samples submitted for analysis were soft tissue (muscle,
organ tissue, and skin), with a small percentage of bone and teeth. Furthermore,
the length of time necessary to perform DNA analysis and identify the victims
of these airline disasters (prior to the American Airlines Flight 587 crash)
was many months, and sometimes years. Thus, when faced with the challenge of
performing DNA analysis on more than 26,000 biological samples (including approximately
13,000 bone samples) recovered from more than 2,700 victims of the World Trade
Center (WTC) attacks, conventional approaches were insufficient and the development
of novel, high-throughput methods was required.
Decisions regarding the identification strategy may have a significant impact
on the success of obtaining DNA results. The medical examiner responsible for
the identification of the remains (and signing death certificates) must decide
whether to analyze remains until all individuals have been identified, analyze
only those remains that are anatomically recognizable, or analyze each remain
recovered. Under normal circumstances, human remains recovered in a mass fatality
incident are taken through a triage-like process in a medical examiner’s facility
by a qualified specialist (e.g., a forensic anthropologist or pathologist).
This process allows for the assessment of the condition of the individual remains,
and the suitability of the remains for DNA analysis. In doing so, a large portion
of the remains is usually determined to be unsuitable for DNA analysis (e.g.,
calcined and moldy samples).
In the case of the WTC identification project, the medical examiner and his
DNA advisors made the decision to test all remains recovered, and then-mayor
Rudolph Giuliani reported this decision to the public. While this decision was
met with skepticism and disagreement in the forensic community, it was based
in part on the anticipated difficulty of finding remains from each individual
lost in the WTC towers. As the project unfolded, it became quite clear that
the decision to do so was correct. Nonetheless, this decision also meant that
a larger percentage of the remains would not produce DNA results. Therefore,
the task at hand was a daunting one: to develop a DNA extraction method that
could handle the rapid processing of thousands of skeletal remains, many of
which were in extremely poor condition, while maintaining the quality necessary
for identifying as many of the WTC victims as possible.
The principal role of The Bode Technology Group in this process was to develop
a quality, high-throughput DNA extraction and short tandem repeat (STR) analysis
procedure for skeletal elements, and to provide STR profiles to the Office of
the Chief Medical Examiner (OCME) in New York City to be used for identification
of the victims.
A high-throughput process was developed to include electronic accessioning
of samples, so that the numbering system of the OCME was maintained; rapid preparation
and sampling of skeletal fragments to allow for the processing of more than
250 fragments per day; use of a 96-well format for sample extraction, DNA quantification,
and STR analysis; and use of the Applied Biosystems 3100 and 3700 instrumentation
to develop STR profiles.
Given the highly degraded nature of the skeletal remains received by Bode,
an advanced DNA extraction procedure was developed to increase the quantity
of DNA recovery and reduce the co-purification of polymerase chain reaction
(PCR) amplification inhibitors. In addition, two new STR multiplexes were developed
specifically for this project, which reduced the amplicon size of the STR loci,
and therefore, enhanced the ability to obtain results from the most challenged
of samples.
In all, the procedures developed allowed for the analysis of more than 1,000
skeletal samples each week. Approximately 13,000 skeletal fragments were analyzed
at least once, for a total of more than 18,000 analyses, and greater than 8,000
of the skeletal samples produced STR results (65 percent). The percentage of
successful results was low in relation to previous mass fatality incidents involving
airline disasters. However, when this same process was applied to the analysis
of skeletal remains from the American Airlines Flight 587 disaster that occurred
on Nov. 12, 2001, the success rate was in line with expected results (i.e.,
greater than 92 percent of the skeletal remains produced results). This illustrated
the quality aspects of the procedure and the degree of degradation that had
occurred for the remains of the WTC victims. For future mass fatality incidents,
the quality, high-throughput procedures developed by Bode will allow for more
rapid DNA analysis of victim remains, more rapid identification of victims,
and thus more rapid return of remains to family members.
The project has gone through two distinct phases thus far, in a focused effort
to identify and re-associate as many fragmented skeletal remains as possible.
Phase I involved rapid DNA extraction of approximately 13,000 bone samples by
using the newly developed and validated procedures. Once the bone samples were
extracted, they were carried through DNA quantification, PCR amplification,
and STR analysis in a high-throughput manner. Bone samples processed during
Phase I generated DNA profiles useful for identification, partial profiles or
no profiles. Those samples that yielded partial profiles were subsequently reprocessed
using a modified version of the Phase I extraction procedures.
Using this molecular triage approach to processing a large number of samples
allowed Bode to report DNA types back quickly to the OCME and concentrate on
samples that could be successfully typed given further laboratory work. Thus,
Phase II of this project involved the re-extraction of more than 5,300 of the
original 13,000 bone samples. This process utilized a modified version of the
initial bone extraction procedure that was geared toward the reduction of potential
inhibitors and the use of larger amounts of input bone material. Along with
this modified extraction procedure, Phase II included the use of a novel pair
of mini-STR multiplexes, which were designed to reduce the amplicon size of
larger STR loci, thereby increasing the chances of obtaining complete STR profiles
from the most degraded bone samples.
While the efforts made during Phase II had a positive impact on the total number
of useful STR profiles available for victim identification, and many of these
profiles led to both re-association of additional remains and identification
of new victims, approximately 45 percent of the WTC victims were not yet identified.
Phase III involves the analysis of individual bone samples on a case-by-case
basis, and may include the re-extraction of bone samples using more traditional
methods, and the use of mtDNA analysis or other advanced techniques, such as
single nucleotide polymorphisms (SNPs). As of June 2003, Bode had spent 20 months
completing Phases I and II of this project, processing and analyzing thousands
of skeletal fragments and soft tissue extracts from samples recovered from WTC
victims.
The attacks on the WTC towers on Sept. 11, 2001, represented the single largest
terrorist-related mass fatality incident in the history of the United States.
More than 2,700 individuals of varied racial and ethnic background lost their
lives that day. Through the efforts of thousands of citizens, including recovery
workers, medical examiners, and forensic scientists, the identification of approximately
1,500 victims had been accomplished through June 2003 (the majority of these
identifications were made within the first eight to 12 months). As the single
largest forensic identification project in the history of the United States,
the WTC disaster has given those involved unprecedented challenges and numerous
obstacles to overcome. The staff of the OCME in New York City is to be highly
commended for their dedication to this mission. The level of creativity applied
to the project, the level of support given to the project, and the unwavering
commitment to complete the project have been unmatched in the forensic community.
Given the number of victims and the daunting number of samples tested, along
with the poor condition of the remains recovered, this project has unquestionably
been a success. While there may be victims of this terrible disaster that will
remain unidentified, it will not be for a lack of perseverance.
Kevin McElfresh wishes to thank Julie Shiroma for her help in preparing
this manuscript. Both authors wish to thank the staff of Bode and the OCME for
their tireless and dedicated work.
Forensic Analysis of Blood Protein and DNA: A Brief History
By Phillip Jones, PhD, JD
According to the Locard Principle of Exchange, when two objects come in contact,
traces from one will be transferred to the other. In violent crimes, a criminal
may leave the scene with traces of the victim's blood, compelling biological
evidence of guilt.
For more than 100 years, forensic investigators looked for the right combination
of blood factors to link a bloodstain to an individual-a blood fingerprint.
This ambition is approaching realization, but in a way that the original investigators
could not have contemplated. But before forensic scientists could begin to consider
analyzing a bloodstain to identify who had shed it, they had to contend with
more basic questions. Is a stain a bloodstain? And if so, then is it human blood?
After a stain is identified as human blood, is there a way to link that blood
to a particular individual? A major medical discovery sparked the hope that
a bloodstain could be used to identify the person who had shed the blood.
The therapeutic method of blood transfusion was often successful; but sometimes,
the patient died. Several hundred years of studies revealed the cause of failure
and provided a significant forensic technique. During the 1660s, Jean-Baptiste
Denys, court physician to Louis XIV, received a patient, a feverish and weak
boy who had been bled by other doctors. Deciding that blood loss was responsible
for the boy's weakened condition, Denys transfused about nine ounces of a lamb's
blood into the vein of the patient. The boy survived. Denys continued to perform
animal-to-human transfusions until he experienced a fatality. Transfusions involving
humans were soon outlawed in large parts of Europe.
About 150 years later, Dr. James Blundell, a London obstetrician, began experiments
with blood transfusion. He found that he could drain almost all of the blood
from a dog and then revive it by transfusing the blood of another dog. On the
other hand, the dog would die if Blundell attempted to revive it with sheep's
blood. When Blundell began transfusing humans with human blood, he found that
his patients occasionally died. Why should transfusion fail with human blood?
The answer started to become clear in 1875 when German physiologist Leonard
Landois noticed that an animal's red blood cells would aggregate and burst if
mixed with the serum of an animal from another species. Significantly, the same
reaction could occur when blood samples from two people were mixed. This suggested
that there were different types of human blood.
In 1900, Karl Landsteiner, assistant professor at the Institute of Pathology
and Anatomy in Vienna, took blood samples from six people, centrifuged the samples
to separate serum from red blood cells, and then mixed red blood cells and serum
samples from different people. In certain mixtures, the serum seemed to attract
the red blood cells, causing the cells to clump together, whereas this reaction
did not occur in other mixtures. He labeled the two blood types A and B. Soon,
he found a third blood type that showed characteristics of both A and B, and
he called this C (later known as type O). A year later, an assistant discovered
yet another type of serum that did not cause aggregation of either type A or
type B blood. This one was called AB, the fourth major blood group.
We know now that, in the ABO system, blood type is determined by the presence
or absence of A antigens and B antigens on red blood cells. If an individual
is type A, then that person's red blood cells have A antigens located on the
surface. Similarly, a type B person has red blood cells with B antigens, whereas
a type AB person has red blood cells with both A and B antigens.
Type O persons have neither A nor B antigens on the red blood cells.
These antigens can stimulate an immune response, including production of antibodies
that bind the antigens. For example, an anti-A antibody binds with red blood
cells that carry A antigens. Since an antibody can bind at least two antigens,
an anti-A antibody can bind with A antigens on two red blood cells. A collection
of anti-A antibodies can create a network of cross-linked red blood cells. The
result: red blood cells aggregate.
The fatal consequence of transfusing incompatible blood is based on this interaction
between a person's antibodies and antigens in the transfused blood. As an illustration,
the transfusion of type A blood into a type O patient can result in the binding
of the patient's anti-A antibodies to the blood cells, causing the cells to
stick together. Transfusion reaction symptoms include red blood cell lysis,
kidney damage, shock, and blood coagulation.
Blood typing takes advantage of these antibody-antigen reactions. In one approach,
blood is tested with anti-A antibodies and anti-B antibodies. Anti-A antibodies
cause clumping, or "agglutination," of type A red blood cells, anti-B
antibodies agglutinate type B blood, both types of antibodies agglutinate AB
blood, and neither type of antibody will agglutinate type O blood.
Other scientists built upon Lansteiner's ABO discovery. In the mid-1920s, Japanese
scientist Saburo Sirai found that blood was not required to determine blood
type: many people secrete blood group-specific antigens into other bodily fluids.
About 80 percent of the human population is secretors, meaning that the specific
types of antigens, antibodies, and enzymes characteristic of their blood can
be found in other bodily fluids and tissues. Investigators can determine a secretor's
blood type by examining saliva, teardrops, skin tissue, urine or semen.
By the end of the 1950s and 1960s, scientists had identified many types of
blood antigens. Yet blood characterization was still more useful to show who
had not shed the blood, rather than point out who had shed the blood. Forensic
serologists lacked sufficient tools to create the elusive blood fingerprint.
There was a glimmer of hope in 1967 when Brian Culliford of the British Metropolitan
Police Laboratory found he could detect the enzyme phosphoglucomutase (PGM)
in dried bloodstains. This enzyme is polymorphic-that is, the enzyme is found
in multiple, distinct forms. The PGM polymorphic forms are inherited and occur
in the population in frequencies useful to the investigator.
Here's how PGM characterization aids an investigation. Consider a bloodstain
that contains the PGM form PGM2-1 and that is type A blood. In the United States,
42 percent of the population have type A blood. Regardless of blood type, PGM2-1
is found in 36 percent of the population. This means that PGM2-1 is present
in type A blood in 15 percent (0.36 x 0.42) of the population. Although blood
samples from different people might have the same blood type or blood enzyme,
it is less probable that two unrelated people have the same blood type and same
form of blood enzyme.
A 1983 investigation illustrates the value of bloodstain analysis. On Oct. 24
of that year, workmen arrived at the Laitner home located in a suburb of Sheffield,
England. They found the Laitner's 18-year-old daughter in a bloodstained nightgown.
She told them that she had been raped and that her parents and brother had been
murdered. Alfred Faragher, who was in charge of a local serology lab, had a
problem: too much blood. But on the daughter's bed, he did find a bloodstain
that appeared about knee level of a person lying in bed. Since the daughter
had no cuts on her knees, the investigator decided that the blood had come from
the killer.
Faragher's team analyzed the bloodstain and found a combination of factors
that should occur in only one person in 50,000. Fortuitously, Faragher recognized
the combination; he had seen it in the blood of a rape suspect that had been
sent to him one month earlier. While in custody, the police had taken a blood
sample from the suspect, Arthur Hutchinson. Faragher's comparison of Hutchinson's
blood with the bloodstain found in the bed strongly indicated that Hutchinson
had killed the Laitners.
Unfortunately, Hutchinson had escaped. He had jumped out of a second story
window of the police station and had climbed a 12-foot wall topped with barbed
wire that had torn open his leg. To flush out Hutchinson, the police spread
reports that the barbed wire had been specially treated and was likely to turn
the suspect's leg gangrenous. The police captured Hutchinson as he made his
way to a hospital. Serological detection, coupled with clever police work, had
led to the identity of an unknown killer.
By the 1980s, about 100 protein polymorphisms had been identified; blood analysis
had come a long way in the century since the famous meeting of Holmes and Watson.
And in the early 1980s, the quest for a technique that could match a person
to a bloodstain took a large step closer to reality.
The Value of Junk DNA
In 1984, Dr. Alec Jeffreys, a research fellow at Leicester University's Lister
Institute, discovered highly repetitive sequences in the genetic code that could
be used to identify an individual. Forensic science has not been the same since.
Before looking at Jeffreys' contribution, let's take a quick hitchhiker's guide
to genetics.
A DNA molecule is a polymer made of linked nucleotides. Nucleotides are composed
of a sugar molecule, a phosphorus-containing group and a nitrogen-containing
molecule called a base. The four types of bases, adenine, cytosine, guanine,
and thymine, are usually designated by the first letter of their names.
Two DNA molecules coil into a double helix with paired bases from each molecule
providing the steps of this spiral staircase. The average human chromosome has
a double strand of DNA containing 100 million base pairs, and all of the human
chromosomes taken together contain about three billion base pairs. This genetic
information encodes every protein made by the body. However, not all nucleotide
sequences code for the production of proteins -- at least 90 percent of DNA
is considered "junk DNA" because it lacks a known function. This junk
DNA contains nucleotide sequences that are repeated numerous times, and although
the significance of the repeats is unclear, forensic investigators find them
useful.
In 1980, scientists discovered hypervariable regions of DNA. These regions consist
of short tandem sequences repeated over and over again, and show extreme variation
between individuals. Jeffreys found that the repeats contain core nucleotide
sequences of 10 to 15 bases. He isolated several core sequences and used them
as probes to detect hypervariable regions in DNA samples that he obtained from
members of a family.
First, Jeffreys treated the DNA samples with restriction enzymes, which recognize
certain nucleotide sequences and cut DNA to produce DNA fragments of various
lengths. Jeffreys then placed cleaved DNA on gels and applied a high voltage
electric current to sort DNA fragments by size. Jeffreys transferred the DNA
fragments from gels to nylon membranes and treated the membranes with a radioactive
marker that binds with target nucleotide sequences. After the nylon sheets were
placed against X-ray sensitive film and the X-ray film was developed, the DNA
fragments carrying the radioactive markers appeared in a series of bars that
look like bar codes. When he compared X-ray film from parents and children,
he found that these bar codes varied between individuals, and that the patterns
were inherited. Jeffreys soon applied his technique in the forensic science
arena.
In the early morning of Nov. 22, 1983, a hospital porter walked along a footpath
on his way to work in the village of Narborough, near Leicester. He discovered
the body of a 15-year-old girl who had been raped and killed. Semen analysis
indicated that the killer was a Type A secretor with the enzyme marker, PGM1.
The two factors occurred together in ten percent of the adult male population,
which helped the police to narrow their suspects. But the investigation led
nowhere.
Three years later, the body of another 15-year-old girl was found within a mile
of the first victim. Semen tests suggested that this was the same killer. A
teenage boy fell under suspicion even though a blood test showed that he was
not a Type A-PGM1 secretor. The authorities contacted Jeffreys, who extracted
DNA from the killer's semen and compared it with DNA obtained from the suspect's
blood. The samples did not match. On the other hand, Jeffreys did confirm that
one man was responsible for both murders.
The police decided that if Jeffrey's DNA typing technique could clear a suspect,
then it might also identify the killer if blood samples were analyzed from the
local male population. Hoping to flush out the killer, they drew blood from
every local male between the ages of 16 and 34 for DNA testing. It worked.
In a Leicester pub, an eavesdropper heard a group of bakery workers discussing
the sexual adventures of an acquaintance named Colin Pitchfork. One of the group
mentioned that Pitchfork had forced him to take the blood test on his behalf.
The eavesdropper passed this information to the police who arrested Pitchfork.
Jeffreys tested Pitchfork's blood and showed that the suspect's DNA was identical
to the DNA of the killer-rapist. Pitchfork was the 4,583rd male to be tested.
The Pitchfork case garnered international attention and DNA typing was hailed
as the most significant development in forensic science since fingerprinting.
A modification of Jeffreys' method became the first accepted protocol in the
United States for forensic characterization of DNA. The technique captured the
public's imagination after an FBI laboratory used it to analyze stains on Monica
Lewinsky's infamous blue dress.
The latest DNA typing technique relies on short tandem repeat (STR) analysis.
STR refers to locations on chromosomes that contain short repeating sequences
of three to seven nucleotides. Human chromosomes have hundreds of different
types of STRs. On each chromosome, the number of repeats varies greatly from
person to person. The probability of two random DNA samples having the same
repeat pattern at a single location in one chromosome is small. The probabilities
become minute after combining results of STR analysis from multiple chromosomal
locations.
DNA typing is often called "DNA fingerprinting," but this term is
misleading. Fingerprints are considered unique to an individual, whereas the
results of DNA typing are expressed as probabilities. A DNA profile probability
indicates the probability that a person chosen at random from a certain population
has the DNA profile of the sample obtained from the crime scene.
The FBI has selected 13 STRs to serve as a standard battery of repeated sequences
for DNA typing. Suppose a DNA sample is obtained from a suspect and analyzed
for all 13 STRs to obtain a DNA profile. The probability that DNA from an unrelated
person will provide the same profile as the suspect's DNA is less than one in
10 billion. Considering that the world's population runs just over six billion,
these results are fairly close to an identification.
Phillip Jones, PhD, JD, is a biotech law specialist and has written more
than 76 articles for magazines, journals and newsletters on a variety of subjects
that blend law, history and science.
12/04/2003
Cal State L.A. Offers Winter Series Focus on Forensic Science
11/25/2003
DNAPrint Announces Forensic Eye Color Results at Amsterdam Forensic Meeting; World's First Genomics-Derived Test For Forensics Investigation With Predictive Capabilities
Orchid Cellmark Awarded FBI Contracts to Develop SNP Technology for Advanced Forensic Applications
11/17/2003
Zebra Technologies and Porter Lee Partner to Fight Crime; CSI Bar Code Application Increases Security While Reducing Time in Tracking Evidence From Collection to Disposition
11/14/2003
LUC Treats Launches Line of Mints/Gum to Help Stop Domestic Violence
New Evidence About the Assassination of President John F. Kennedy Revealed
11/11/2003
Study Documents Law Enforcement Efforts Combating Internet Sex Crimes Against Children
More News
|
