DNA Evidence and Forensic Science in Solving Cold Cases

Introduction

Shortly after dawn on Tuesday, November 22, 1983, the body of a fifteen-year-old girl was found brutally raped and strangled on a narrow dirt footpath near the English village of Narborough in Leicestershire. Her name was Lynda Mann. A semen sample taken from her body was found to belong to a person with type A blood and an enzyme profile that matched only 10% of the adult male population. Even though a massive manhunt was launched, the case remained unsolved. Three years later the killer struck again, this time killing fifteen-year-old Dawn Ashforth in almost the identical spot where Lynda's body was found. Semen samples recovered from Dawn's body revealed her attacker had the same blood type as Lynda's murderer. Even though police knew the murders were committed by the same man, it took four years, a scientific breakthrough, and blood samples from more than four thousand men before the real killer was finally brought to justice (Lee, 1993).

Solving a murder is never easy. For the most part, unless law enforcement officials obtain a confession, it is often difficult to make an arrest and even harder to obtain a conviction without eyewitness testimony or compelling DNA evidence. Many television shows like Law & Order and CSI have glamorized the effectiveness and efficiency of the latest advances in forensic science, including the application of DNA matching to link murderers to their victims. Within the space of an hour, these fictional detectives solve murders that could take years to resolve, even with the best scientific minds working around the clock. On TV, the police always find DNA samples that are uncorrupted and rush them to a lab for near-instant processing. The bad guys always leave something behind: a partial thumbprint on a nightstand, skin under the victim's fingernails, even trilobal carpet fibers later matched to the trunk of the murderer's car.

In the real world of forensic science, things are not always so straightforward. DNA was not used to solve criminal cases until the 1980s. The first murderer to face justice based solely on DNA evidence found at a murder scene was Colin Pitchfork, who in 1988 was sentenced to life in prison for the murders of Lynda Mann and Dawn Ashforth.

This research paper explains what DNA is and how it is used to solve criminal cases. It discusses the implications of DNA fingerprinting in solving cold cases, with a focus on collection methods and applications in the state of California. This research analyzes the feasibility of DNA testing in solving cold cases and studies the impact that DNA fingerprinting has had on the forensic science community as a whole. The research is driven by studies and collection methods already implemented by the scientific community, as well as future methods of collecting and testing DNA evidence as they relate to the investigation of unsolved murders.

Defining DNA and the CODIS Database

DNA is generally used to solve crimes in one of two ways. In cases where a suspect is identified, a sample of that person's DNA can be compared to evidence from the crime scene. The results of this comparison may help establish whether the suspect committed the crime. In cases where a suspect has not yet been identified, biological evidence from the crime scene can be analyzed and compared to offender profiles in DNA databases to help identify the perpetrator. Crime scene evidence can also be linked to other crime scenes through the use of DNA databases.

In the late 1980s, the federal government laid the groundwork for a system of national, state, and local DNA databases for the storage and exchange of DNA profiles. This system, called the Combined DNA Index System (CODIS), maintains DNA profiles obtained under federal, state, and local systems in a set of databases available to law enforcement agencies across the country. CODIS can compare crime scene evidence to a database of DNA profiles obtained from convicted offenders. It can also link DNA evidence obtained from different crime scenes, thereby identifying serial criminals (Lee).

In order to take advantage of the investigative potential of CODIS, states in the late 1980s and early 1990s began passing laws requiring offenders convicted of certain offenses to provide DNA samples. When used to its full potential, DNA evidence may help solve — and may even prevent — some of the nation's most serious violent crimes. However, the current federal and state DNA collection and analysis system faces significant challenges:

According to a recent article in Corrections Today magazine, "DNA evidence is one of the most powerful crime-fighting tools since the advent of latent fingerprint technologies. It has the ability to convict the guilty and free the innocent" (Wilson et al., 1999). DNA is an acronym for deoxyribonucleic acid, a double-helix molecule found in the nuclei of cells. DNA is the basic building block of life and is based on the arrangement of four chemicals. "The arrangement of the three billion pairs of bases in each DNA molecule is different for everyone (except identical twins). An individual's DNA is the same in every cell, from the moment of conception to death. A person's DNA in scraped skin cells will be the same as the DNA in his blood, saliva, organs, semen, or hair" (Wilson et al.).

"On April 25, 1953, nine hundred words changed the world. Those words constituted the brief report by James Watson and Francis Crick that appeared in the renowned science journal Nature. They began, 'We wish to suggest a structure for... DNA. This structure has novel features, which are of considerable biological interest.' They ended just as modestly: 'It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for genetic material'" (Lee). In 1991, nearly 40 years after the Nature article was published, Watson wrote, "There is no substance so important as DNA... The key to our optimism that all secrets of life are within the grasp of future generations of perceptive biologists is the ever accelerating speed at which we have been able to probe the secrets of DNA" (Lee).

The Discovery of DNA

"Earth's biological past is a four-billion-year journey of the evolution of living organisms, all of which, in each of their cells, harbor long, densely coiled strands of DNA molecules. These serpentine coils are gathered into discrete bundles, the chromosomes. Along the length of each chromosome, the genes (perhaps as many as 100,000 in a human being) are each a unique segment of the chromosomal DNA. The precise details of the molecular structure of the DNA in each gene spell out a genetic code. The cells read the code and respond to its commands" (Lee). The result of this process is life itself.

It has always been obvious, even to the non-scientific mind, that all living creatures have special attributes that set them apart from other things — growth, movement, and reproduction. All forms of life appear to generate others that share these same attributes. Scientists wanted to know how each living creature could be unique, yet still share in "this mysterious common denominator, life" (Lee).

As science continued to ask and answer questions about DNA, the tools of investigation became more sophisticated. Scientists were eventually able to dig deeper into the mystery surrounding cells. "They finally arrived at the cell nucleus, the membrane-bound sac enclosing the chromosomes. Going further, they learned how to extract and study the chromosomes themselves. The chromosomes turned out to be fashioned out of DNA and proteins" (Lee).

When Watson and Crick presented their study of DNA to the scientific community, "they did much more than describe the three-dimensional symmetry of just one of the thousands of chemicals found in living cells. They had uncovered the secret which would soon lead to a New Biology, in which the evolution and abilities of each living creature would be seen precisely as the result of information flowing from its genes — messages carried not in the nuclear proteins but in the molecules of DNA" (Lee).

After this discovery, the biological sciences quickly centered on genes. "The applications of this new approach are already beginning to reach into almost every facet of our lives in ways which range from life-saving gene-based diagnostics and treatment to the fashioning of hitherto impossible new genetic forms of animals and plants. Scientists are already well under way on the Human Genome Project, a 15-year-long effort to construct a map locating the 100,000 or so genes which are spread out over our 23 pairs of chromosomes and which spell out the genetic directions for the human race" (Lee).

Along with the powerful knowledge that scientists have gained through the discovery of DNA comes a responsibility that many say most humans cannot yet fathom. "Knowledge may not always lead to power, but it is certainly a critical prerequisite to making an informed decision about issues which surface where science and society meet. We are facing a change which could surpass the Industrial Revolution in its impact on the world" (Lee). Indeed, the terms gene and DNA have become part of the American vernacular. Rarely a day passes when the word DNA does not appear in a newspaper headline or magazine article. In recent years, genes for diseases like cystic fibrosis or certain forms of cancer have been identified, and legal battles over whether courts should accept DNA evidence in criminal cases have become commonplace.