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Amazing Advances
in Forensic Science Part 1: DNA |
Introduction
Practical Homicide Investigation® emphasizes that the basic time-proven traditional investigative methodologies, which have been used by law enforcement throughout the years be coupled with an appreciation for and an understanding of the advances in forensic science and its application to the investigative process. Forensics, which is the application of science to matter of law, has made great strides over the last thirty years providing law enforcement with an assortment of exciting tools.
Forensics has made great strides over the last 30 years, providing law enforcement with an assortment of exciting tools. The forensic sciences include the disciplines of pathology, toxicology, serology and forensic DNA analysis, psychiatry, psychology, entomology, odontology, computer and digital science, archeology, anthropology, geology, etc.
Criminalistics is the application of various sciences to answer questions relating to the examination and comparison of biological, trace and impression evidence, such as fingerprint analysis, footwear, tire impressions and toolmark evidence, as well as drug analysis, ballistics and firearm examinations.
However, the greatest advancement in the forensic sciences is the application of DNA technology to the criminal justice process. DNA typing is a powerful tool because proper analysis and collection can convict the guilty and exonerate the innocent. Procedural improvements have made the collection of DNA evidence more efficient and reliable, and advances in science allow forensic scientists to identify DNA samples from hair, bone, and ever smaller amounts of blood and other body fluids.
The Start: Blood Groups
I remember conducting and supervising homicide investigations in the late 1970's and early 1980's before we had DNA technology and all of the advanced criminalistics capabilities that we have today. All we had to work with prior to these fantastic advances were the ABO blood group system, which had been discovered by the Austrian scientist Karl Landsteiner in 1901. It wasn't until the late 1970's the serologists, because of the limitations of the ABO system, began to look at biochemical markers. Forensic scientists were examining enzymes found on the red cell membrane. These PGM's (Phosphoglucomutase) or genetic markers were protein enzymes which were found throughout the entire body. The PGM1 was also found in semen, which increased its value in forensic serology because of two alleles. Designated "1" and "2" PGM-1, PGM-2 PGM 2-1. This discovery of three phenotypes, which provided additional genetic information about the blood or sperm recovered from a crime scene, was an exciting forensic advance in the early 1980's.
This progress took on speed with the scientific analysis of Deoxyribonucleic Acid (DNA) It was learned that certain areas of DNA vary quite dramatically from one individual to another individual and that these polymorphic regions are so unique to each individual that this technology could be used as a forensic tool.
It wasn't until 1986 that the first forensic application of DNA typing was performed by Dr. Alec Jeffries in England, who was able to match the DNA of a suspect to the biological materials recovered from the bodies of three lust murder victims. The first use of DNA Typing in the U.S. Courts was the Tommy Lee Andrews case involving a series of rapes in Orange County, Florida in November of 1987. This was followed by the Serial Murder case in Virginia of Timothy Wilson Spencer. (1984-1987). Timothy Spencer was the first Appellate Division ruling on DNA and was the first execution based on DNA. However, DNA wasn't always considered such a precise and powerful weapon.
First DNA Murder Case in New York State
In February, 1987 Vilma Ponce, who was eight months pregnant, and her two year-old daughter Natasha Otero were found slaughtered in their apartment 3415 Knox Place, Bronx. Vilma was lying on the living room floor. She was nude from the waist down and her maternity top was pulled up to expose her stomach and lower torso. The woman had been stabbed Sixty-one times. Her daughter, Natasha had been stabbed twelve times. The fetus had also received three stabbing injuries through the womb. I was present at the scene as the commanding officer of The Bronx Homicide Task Force. During the crime scene process, we noticed bloody sneaker prints throughout the apartment as well as droplets of blood over the sneaker prints as well as numerous blood spatters. A single drop of blood found near the front door of the apartment, suggested that the offender might have cut himself. I had been in contact with a microbiologist friend over the years, who kept me up to date with the evolution of DNA technology. He had recently become the director of Lifecodes Corporation, which was a DNA laboratory.
I decided to have the blood evidence in this case taken to this private lab for this new technique called The DNA-Print Identification Test. Within 48 hours we had developed a viable suspect, who had a fresh cut on his hand as well as dried blood on his wrist watch. The suspect, Joseph Castro, agreed to be interviewed and provided an extensive alibi for the day of the murder. He also gave the detectives permission to have his watch examined. At this point there wasn't enough evidence to hold Castro and we did want to keep an open dialogue. The detectives thanked him for his cooperation and drove him home.
This first generation of DNA technology was the RFLP Multi-locus type of DNA analysis, which positively identified Joseph Castro as the killer and he was arrested on March 5, 1987. One month after the vicious and wanton slaying of this young pregnant mother and her two-year-old daughter.
The Court Disposition
People v Castro was the first case that seriously challenged a DNA profile's admissibility. The New York Supreme Court, in a 12-week pretrial hearing, exhaustively examined numerous issues relating to the admissibility of DNA evidence. Attorney Barry Scheck who at the time represented the Public Defender's office, attacked the science of DNA, which resulted in a number of Pretrial hearings are required to determine whether the testing laboratory's methodology was substantially in accord with scientific standards and produced reliable results for jury consideration. The court ruled that the DNA tests could be used to show that blood on Castro's watch was NOT his. But the DNA tests could not be used to show that the blood was that of his victims. However, the defendant was found guilty. I decided to share this exciting new technology with others in law enforcement.
In July, 1988 Law and Order published one of the first articles on the use of DNA for criminal investigations. I had written an article entitled; "DNA Print Identification Test Provides Crucial Evidence In a Lust Murder Case," which illustrated how we had used this new technology to identify the killer. Look where we are today two decades later.
DNA Testing Today
Since then, millions of forensic DNA tests have been conducted in the United States and around the world. In a major advance, the analysis of DNA has evolved from a laborious process taking weeks or even months to a procedure that can be completed in a matter of days. The DNA molecule can establish the link between evidential DNA with that of the possible suspect's DNA. It can identify whether the DNA in question is human or non-human and can be used to establish the sex of the specimen.
The RFLP technology of the 1980's, which was the Model T-Ford of DNA analysis, involved the process of identifying the polymorphic regions that are unique to each individual. These Variable Number of Tandem Repeats or VNTR's contained fairly large repeat units with allele sizes being thousands of base pairs long.
The PCR Breakthrough
In 1993 Dr. Kary Mullis received a Nobel Prize for his work during the 1980's that resulted in the invention of with The Polymerase Chain Reaction (PCR), which mimicked the cell's ability to replicate DNA, which enable scientists to take small samples of DNA and essentially copy it a million fold. All the PCR steps have similar basic steps as in RFLP, extraction, amplification and detection. Additional research identified much smaller VNTR's, which were only a few base pairs long, which coupled with PCR was the advent of STR Technology.
PCR Amplification
PCR amplification allows production of many copies of the region of DNA interest. PCR works like a "molecular xerox machine." Millions of copies of a particular sequence of DNA can be made in about 3 hours in a thermal cycler. This is great for Forensic DNA where there is usually very little DNA to start with. Initially, DNA samples that were small or degraded were beyond the reach of DNA-typing techniques. Saliva found on the back of licked postage stamp or an envelope can provide enough genetic material to conduct a sophisticated DNA test. In a Cold Case DNA ruse, the police sent the suspect a letter from a mock law firm with an invitation to join in a bogus class-action suit. The suspect replied to the letter, providing a DNA sample by licking and mailing the enclosed envelope. The DNA found in the saliva on the envelope matched a sample taken from the victim's body. This couldn't have been done without the benefit of STR/PCR technology.
Mitochondrial DNA (mtDNA)
The Mitochondrial DNA genome has been completely sequenced and is 16,569 base pairs in length. Mitochondria contain their own DNA. Every cell in the human body contains hundreds of mitochondria, which are the power plants of the cells. There are many more copies of mtDNA than nuclear DNA present in the cell. The advantage of mtDNA typing over nuclear DNA is the added sensitivity in cases where nuclear mtDNA allows for the examination of bone fragments, hair without root, teeth & other biological evidence that may be limited.
The amount of mtDNA isolated from such specimens may be very small so DNA extraction is followed by PCR amplification. This allows production of many copies of the region of mtDNA of interest. After the amplification is complete the is mtDNA sequenced using conventional sequencing methods.
Short Tandem Repeats (STR)
The STR class of polymorphisms has become the backbone of modern forensic testing. Short Tandem Repeats (STR) loci are polymorphic genetic markers that are well distributed throughout the human genome. The advantage of STR technology is that the small size of STR loci improves the chance of obtaining a result. The interpretation of STR types is simplified through the use of computers, which analyze the sample. DNA profiling uses high throughput instrumentation equipped with detectors.
Fluorescent detectors identify thirteen different loci that can be analyzed simultaneously. These 13 loci include: D3S1358, vWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317, D7S820, D16S539, Th01, TPOX, and CSF1PO. These 13 loci Form the basis of the National DNA network, CODIS (Combined DNA Index System), which is administrated by the FBI and is installed in forensic laboratories nationwide.
DNA technology is constantly evolving though new applications and innovations. Forensic scientists are combining advances in miniaturization and microchip technologies with well-established techniques of forensic DNA analysis. The fusion of these technologies could revolutionize DNA typing. New methods of DNA technologies have provided for the analysis of previously unsuitable case work samples that are able to be tested.
The Amelogenin Gene
The Amelogenin gene (AAAGTG), is used to identify the sex of an origin of a sample. The standard CODIS set includes amelogenin markers for X and Y chromosomes. If both X and Y are in a sample it is a male. If there is no Y marker, it's a female.
Y-STR DNA
Y-STR-DNA allows for the typing of a portion of the Y chromosome. It detects male DNA only. Small amounts of male DNA can be typed successfully. Mixtures of male DNA (Multiple rapists or rapist with consensual partner) can be resolved and mixtures of male and female DNA may be resolved.
Single Nucleotide Polymorphisms (SNP's)
In order to make new cells, an existing cell divides itself in two. But first it copies its DNA so the new cells will each have a complete set of genetic instructions. Cells sometimes make mistakes during the copying process - kind of like typos or mutations. These typos lead to variations in the DNA sequence at particular locations called Single Nucleotide Polymorphisms or SNP's.
The SNP's are being used to perform DNA profiling of the Y chromosome. In addition to the 13 CODIS loci a number of laboratories have developed multiplexes of SNP's so that male DNA can be individually typed.
Touch DNA
The Touch DNA method was named for the fact that it analyzes skin cells left behind when assailants touch victims, weapons or something else at a crime scene. Humans shed tens of thousands of skin cells each day. These cells are transferred to every surface our skin contacts, i.e. gun grips, eating utensils, steering wheels, etc. If a perpetrator deposits a sufficient number of skin cells on an item at the scene there may be Touch DNA. Touch DNA is not Low Copy Number (LCN) DNA. LCN DNA profiling allows a very small amount of DNA to be analyzed, from as little as 5 to 20 cells. The small amount of starting DNA in LCN samples requires many more cycles of amplification.
Collection of Buccal Cells for DNA Analysis
DNA technology has become so advanced through the extreme sensitivity of techniques like PCR that DNA from epithelial cells that are present in saliva can be swabbed from the surfaces of the oral cavity of suspects. This has become the method of choice in screening a number of suspects in an investigation because the samples can easily and quickly analyzed. During the BTK investigation Kansas detectives collected over 4000 buccal cell samples to compare with their suspect evidence DNA.
SNP Based Ancestry Markers - Biographical Ancestry
Ancestry informative markers are being used by certain DNA firms to help people trace their genographic roots. This technology also has the potential of identifying the four main continental population groups, such as sub-Saharan African, East Asian, Indo-European, and Native American. This technology and could be utilized to allow investigators to concentrate on the specific physical characteristics of the donor of DNA evidence.
CODIS
CODIS stands for Combined DNA Index System. It is the core of the national DNA database, established and funded by the Federal Bureau of Investigation (FBI), and developed specifically to enable public forensic DNA laboratories to create searchable DNA databases of authorized DNA profiles. The CODIS Unit manages the Combined DNA Index System (CODIS) and the National DNA Index System (NDIS) and is responsible for developing, providing, and supporting the CODIS Program to federal, state, and local crime laboratories in the United States and selected international law enforcement crime laboratories to foster the exchange and comparison of forensic DNA evidence from violent crime investigations.
CODIS software enables State, local, and national law enforcement crime laboratories to compare DNA profiles electronically, thereby linking serial crimes to each other and identifying suspects by matching DNA profiles from crime scenes with profiles from convicted offenders.
CODIS uses two indexes to generate investigative leads in crimes for which biological evidence is recovered from a crime scene. The convicted offender index contains DNA profiles of individuals convicted of certain crimes ranging from certain misdemeanors to sexual assault and murder. Each State has different "qualifying offenses" for which persons convicted of them must submit a biological sample for inclusion in the DNA database. The forensic index contains DNA profiles obtained from crime scene evidence, such as semen, saliva, or blood. CODIS uses computer software to automatically search across these indexes for a potential match.
The success of CODIS is demonstrated by the thousands of matches that have linked serial cases to each other and cases that have been solved by matching crime scene evidence to known convicted offenders.
Vernon J. Geberth, M.S., M.P.S. is the author of the Practical Homicide Investigation: Tactics, Procedures, and Forensic Techniques, FOURTH EDITION and Sex-Related Homicide and Death Investigation: Practical and Clinical Perspectives SECOND EDITION CRC Press, LLC. These materials are excerpted with Geberth's permission and are protected under U.S. Copyright Laws.
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