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Back to Archives | Back to November 2007 Contents 

The Impact of DNA on Policing: Past, Present, and Future

By Raymond J. Prime and Jonathan Newman, Centre of Forensic Sciences, Toronto, Ontario, Canada


he 20th anniversary of the first use of DNA1 to assist in a police investigation has passed without fanfare or recognition. In any other business, an event of this importance would have been saluted with public announcements and celebration; however, until the recent explosion of popularity of forensic science on television, the field commanded very little public attention. Nevertheless, the various applications of DNA analysis have cemented a binding partnership between police services and forensic sciences that has changed the justice system in a way that no other investigative tool has before.

DNA analysis has significantly improved police investigations by providing the potential to contribute to investigations in the following ways:

  • Solve particularly difficult cases where all other investigative techniques have failed

  • Provide clues where there are no witnesses

  • Find application in an ever-widening range of cases

  • Reduce the number of wrongful arrests

  • Increase the reliability of evidence

  • Link together cases that otherwise could not be connected, such as local cases ranging from breaking and entering to homicide, multijurisdictional cases such as gang crimes, serial sexual assaults or murders, and major international investigations


The First Use of DNA

DNA analysis was introduced into policing in 1986 when officers from a local police service in a small borough in central England approached Dr. Alec Jeffreys of the University of Leicester to ask whether this new technology might be able to assist in the investigation of two potentially linked sexual assault murders of two young girls.2 Jeffreys analyzed samples from the deceased girls and developed DNA profiles of the perpetrator in each crime, which were found to be identical. A suspect who had confessed to one of the crimes was found to have a different DNA profile; it is an interesting sidebar to this story that the first application of DNA in a police investigation resulted in the exoneration of the confessor to the crime.3 To this day, DNA continues to eliminate suspects who might have otherwise been convicted and identifies those who might be wrongfully incarcerated.

With the DNA results obtained by Jeffreys in hand, the local police organized a collection of blood samples from all 5,000 males in the small community in Leicestershire where the crimes had occurred. These samples unfortunately did not directly identify the suspect, because he was able to convince a friend to stand in for him. However, when the friend eventually confessed the ruse, the police had their suspect. Faced with the DNA evidence, Colin Pitchfork confessed his guilt.

While clearly an exciting time within the circles of forensic sciences and policing, the reality of the early days of DNA technology was that the technique could be applied only to the most serious cases. In the beginning, the availability of technical specialists was limited, the sample size needed for the RFLP analysis4 was rather large, and the length of time needed to complete the laboratory analysis narrowly restricted the application of the technique. However, once the impressive value of this service had been demonstrated to the justice system, technology was soon developed to improve the speed and sensitivity of the testing. These advancements quickly led to the widespread application of DNA testing in criminal investigations.


Investigative Benefits of DNA Analysis

The judicious application of forensic science early in an investigation can lead to the development of investigative information that can save money, time, and resources for police agencies. The whole investigative process can be shortened by the influence of such analysis on the direction of an investigation, by providing information that can be used to enhance conventional interrogative strategies and by limiting the contesting of the evidence in court. In many instances, trials are shortened or the need for a trial is eliminated altogether, further saving resources that can instead be deployed elsewhere, both for the police and the broader justice system. In instances of a guilty plea resulting from compelling evidence, the benefit is not limited to monetary savings: victims are spared the emotional burden of reliving the crime at trial.

In the spring of 2003, 10-year-old Holly Jones went missing from her Toronto neighborhood. The day after her disappearance and over the next few days, parts of her dismembered body were located on the shores of Lake Ontario. These were identified by DNA typing. In addition, a foreign DNA profile potentially belonging to the perpetrator was developed from fingernail scrapings.

The investigation of this case was a huge challenge for the Toronto Police Service; however, lead investigators recognized that forensic science could play a crucial role. Faced with the daunting task of door-to-door canvassing of hundreds of possible sex offenders and more than 2,000 tips from the general public, the traditional police investigation was considerably assisted by information provided by the forensic science laboratory. First, an examination of tapings of the victim by a trace evidence scientist provided the clue that the child had been in contact with a green carpet. During the door-to-door canvassing by front-line police officers armed with this information, a potential suspect was identified. After this person refused to volunteer a DNA sample, undercover police surveillance facilitated the collection of a discard DNA sample for comparison to the foreign DNA profile that had been developed. The profiles matched, the suspect was arrested, and his apartment was searched. DNA analysis revealed traces of the victim’s blood. Faced with the evidence, the suspect confessed and entered a guilty plea.

Prior to the development of DNA analysis, it was not uncommon, especially in cases of sexual assault that caused considerable anxiety to the general public, that the police, working to alleviate community concerns, would make an arrest only to find that their evidence was not sufficient to proceed to trial; in some instances this would result in suspects filing civil lawsuits against the police. Also, when an investigation has apparently ended in the apprehension of the wrong suspect, valuable time is lost at the critical early stages of the investigation. Police now rely on DNA analysis in cases such as these and, with appropriate use of resources, it is possible to execute an arrest after the laboratory has completed the testing. It is now technologically feasible to generate DNA results in less than 48 hours, when necessary.


DNA Databanks

With the creation of state and national DNA databanks, investigators have another important tool that can provide investigative information. Although jurisdictions differ in the types of offenses that qualify for inclusion in their databanks, there is no doubt that these resources are helping to solve crimes that would have otherwise been left unsolved. In England, where the first national DNA databank was created, samples can be collected for all offenses on arrest; therefore, England has the largest per capita databank in the world. As the value of these databanks has become apparent, legislators continue to broaden the base of qualifying crimes, and some jurisdictions have enacted legislation requiring samples from all felons.

The benefit of Canada’s National DNA Databank was demonstrated within months of its creation. A murder case that had remained unsolved for 12 years and had encompassed more than 1,000 suspects was reinvestigated due to the advent of the DNA databank. When the perpetrator’s DNA profile was loaded into the databank as a result of his incarceration from an unrelated conviction, police investigators were provided with the information with which to solve the crime. Due to the passage of time, prosecutors had to rely on the DNA results as the cornerstone of their evidence at the trial, in which the individual was found guilty of the murder.

DNA analysis also provides police investigators with not only the ability to develop leads for current active cases but also the opportunity to return to older, unsolved investigations. By working in partnership with scientists in the forensic science laboratory, investigators can review evidence that might have been collected for another purpose or that might have been of limited value when examined by the conventional technologies available at the time of the original investigation.

In Ontario, one such case was that of Linda Shaw, a young university student who was abducted, raped, and murdered in 1990 as she returned from an Easter visit home using one of the province’s busiest highways. Her death had a considerable impact on many young women who often traveled alone, and it remained unsolved for 15 years. Knowing that a DNA profile of the perpetrator had been developed from samples taken from the victim, an investigator from the Ontario Provincial Police reviewed evidence items and found that early in the investigation, hair samples had been collected from 40 persons of interest for microscopic hair comparison. Knowing also that present-day techniques allow for DNA extraction from a hair root sheath, the investigator asked the forensic biologist whether the hair samples could be tested. A microscopic examination showed that DNA analysis was possible for 20 of the hair samples, and a matching profile was developed from one of them. The perpetrator was identified as an individual who had committed suicide many years before, after he had been arrested on an unrelated matter.

By working in partnership with forensic scientists, police investigators can develop systematic plans for the reexamination of unsolved serious crimes. This has the value of providing a level of comfort to the victims or their families, an appropriate penalty to the accused on conviction, and, in some cases, preventing the commission of further crimes.

Working with the laboratory provides investigators with sound scientific advice for selecting the most appropriate samples for testing; often, the laboratory can assist in locating the evidence samples. Mary Jane Burton, a Virginia forensic scientist, is known for having meticulously saved samples cut from the evidence items in her case files.5 These have recently been used to reopen investigations and exonerate wrongfully convicted individuals many years after Burton’s death. Ironically, this practice is forbidden in a modern–day, accredited laboratory environment; however, it has been replaced by more appropriate practices for storing, locating, and identifying potential evidentiary materials for future examination.


Applying DNA to High-Volume Crimes

Recognizing that property crimes such as breaking and entering form a significant proportion of crimes committed and that serious offenders either started with committing, or continue to commit, breaking and entering, police services are increasingly requesting that DNA technology be applied to these high-volume crimes. Some laboratories are able to respond by using robotic instruments to assist in the DNA analysis of items from such cases.

Robotic systems provide a solution for the processing of large numbers of samples, but there is usually a requirement to standardize the type of sample that the system can handle, in both the type and the amount of material available. A possible sacrifice of sensitivity resulting from standardization must be weighed against the ability to increase the workflow. These are issues that laboratories continue to address through research and development.

The British were the first to demonstrate the value of using DNA analysis with high-volume crimes by pointing to the high success rate of either identifying suspects or links to other crimes. Jurisdictions in the United States and Canada have followed suit and report that links between the crime and a profile in the databank occur in approximately one of every five cases submitted to the laboratory for DNA testing, providing leads to police officers who would otherwise have little chance of solving certain offenses without the application of considerable investigative resources.

As crimes are linked together, the opportunity increases for police to identify other accomplices and file appropriate charges. Many point to the value of identifying perpetrators early in their criminal careers, noting that it is not uncommon that most who commit serious crimes have some history of involvement in lesser criminal activity such as burglary or car theft.


Mixed DNA Profiles

One of the difficulties associated with DNA analysis is that if a sample contains DNA from more than one individual (known as a mixed profile), the profiles cannot be easily separated, reducing the overall success of the testing. The solution to this problem will be aided by the ongoing development and refinement of computer software to assist scientists in reaching objective and unbiased interpretations. In the future, continued improvements in technology will permit laboratories to process more samples and improve their ability to interpret mixed profiles.

A common example of a mixed profile is that obtained in a sexual offense in which semen is recovered from the body of a woman. In some circumstances, the DNA contribution from the female may be far greater than that of the male perpetrator. To date, forensic scientists need to take advantage of physical/chemical properties of the sample and their own interpretation skills to generate profiles specific to the male contributor. Where there is only a trace amount of DNA from the male or where there is more than one male contribution, it is not always possible to generate a result from the perpetrator that can be utilized in the investigation.

However, a new technique being applied more extensively in such cases is Y-STR analysis. The Y chromosome is a male-specific identifier, and typing techniques are now available that develop profiles specific to the male contributor of the DNA. The advantage of this test is in its high level of sensitivity; the test is able to generate a profile of a male perpetrator in the presence of DNA from a female contributor.

A limitation of Y-STR analysis is that the DNA profile obtained will be identical for all males within the same paternal lineage (i.e., the father’s profile will be the same as that of his son, whose profile will also match that of his grandfather on his father’s side, and so on). The continuity through the family lineage is useful when attempting to identify an unidentified person. If investigators suspect that unidentified remains are those of a missing man who has a son, they can compare the Y-STR profile from the unidentified remains with that of a sample provided by the son. Mitochondrial DNA (mtDNA), which is inherited through the maternal line, is used in a similar way. This technique has additional applications in relation to the investigation of criminal cases and will be used more extensively with the development of more laboratories equipped to perform mtDNA testing.

Both Y-STR and mtDNA are restricted to specific applications where conventional STR analysis cannot be used. They are not compatible with existing DNA databanks. For this reason, a decision to consume the last small portion of a sample for this type of testing must be taken in consultation with the laboratory and with careful consideration of its value.


Future Tests

Some of the challenges for the future will test the balance between the needs of the law enforcement community and the public’s interest in preserving its own civil liberties. Techniques are currently under development that will enable the prediction of some physical traits through DNA analysis, providing police with a potential genetic “eyewitness.” In addition, databanks are being used to identify perpetrators through kinship relationships to relatives whose profiles may already be included in a DNA databank; this use of the technology is raising moral and ethical questions about such applications.

With the increasing mobility of national populations and concerns to curtail international crime and terrorism, the law enforcement community will desire to make databanks more readily accessible. By analogy, Canada and the United States recently developed an agreement to link their Integrated Ballistics Information System (IBIS) databases. This can be done more easily than with DNA databanks, which are affected by the laws and principles of each jurisdiction surrounding the use of personal information associated with an intimate sample, such as a person’s DNA.

Since the introduction of DNA evidence, it has played a key role in the investigation of numerous crimes; police now rely on DNA analysis to provide intelligence that was previously unavailable. The compelling evidentiary value of this technology has resulted in an increased expectation of impartial scientific evidence in the courts. It has been used as a part of impartial reviews of postconviction cases, and its convincing discriminatory ability has been instrumental in demonstrating support for exonerations and convictions alike.

Through partnerships between police and scientists, DNA analysis will continue to be regarded as the standard of excellence for the development of impartial, unbiased scientific evidence in the support of the justice system.■


Notes:

1DNA stands for deoxyribonucleic acid, one of the two types of molecules that encode genetic information. The other is ribonucleic acid (RNA). The first proof that DNA was the substance in which hereditary traits were encoded was provided in 1944 by Oswald Avery, Maclyn McCarty, and Colin MacLeod. The double-helical structure of DNA was discovered in 1953 by James D. Watson and Francis H. C. Crick with the invaluable collaboration of X-ray crystallographer Rosalind Franklin. Watson and Crick shared the 1962 Nobel Prize in Physiology with Maurice H. F. Wilkins.
2Sir Alec John Jeffreys, British geneticist (b. 1950), was educated at Oxford University, where he completed his Ph.D. in 1975. Conducting his research at the University of Leicester, he developed the technique known as genetic (or DNA) fingerprinting. In 1986 he assisted police in analyzing the DNA from two sexual assault murders and is credited with being the first to use genetic fingerprinting in a criminal case. Jeffreys was elected a Fellow of the Royal Society in 1986, appointed as a Royal Society Research Professor in 1991, and knighted in 1994. In 1996 he was awarded the Albert Einstein World Award of Science. For additional information on Jeffreys’s work see Alec J. Jeffreys, “Genetic Fingerprinting,” Nature Medicine 11, no. 10 (October 2005): xiv–xviii, http://www.laskerfoundation.org/awards/naturemedicine/jeffreys_NM.pdf (accessed September 25, 2007).
3This suspect was a 17-year-old mentally challenged kitchen porter at a mental hospital, who had confessed to one of the murders. Through the acceptance of the DNA evidence, the same investigators who took him into custody worked to have him released. Details of the investigation, identification, and prosecution are presented in former Los Angeles police officer Joseph Wambaugh’s book The Blooding (New York: Perigord Press, 1989).
4In the early use of DNA, crime laboratories relied primarily on Restriction Fragment Length Polymorphism (RFLP) testing, a technique that is very discriminating but requires a comparatively large quantity of good-quality DNA. Today, the technology has advanced, enabling quicker testing with a smaller sample using a technique known as short tandem repeats (STR) typing.
5Mary Jane Burton (d. 1999) was an employee of the Virginia Department of Forensic Science. Years after her death, a simple procedure she had followed in each case would assist in exonerating persons wrongly convicted of crimes. In laboratory files, Burton would save a small sample—a cotton swab, a piece of clothing, or anything that contained the suspect’s bodily fluids—from any laboratory tests she performed. This procedure came to light in the case of Marvin Anderson, who had been convicted of rape in 1982 and was granted parole in 1997. In 2001, Anderson learned of DNA testing and, believing it would clear his name, contacted the Innocence Project, which in turn contacted the Virginia authorities. The state forensic department pulled Anderson’s laboratory file and found a cotton swab attached to the blood work report completed by Burton. The state conducted a DNA test on the cotton swab, and the results established that Anderson was not the rapist. Marvin Anderson received a full pardon in August 2002. Other cases were reviewed later, and Burton’s standard procedure of always keeping a sample has cleared two other persons convicted of crimes. See Kristen Gelineau, “Saved from the Grave,” MSNBC, October 16, 2005, http://www.msnbc.msn.com/id/9666591/ (accessed September 25, 2007), and Frank Green, “Scientist’s Legacy: Freedom for Two,” Richmond Times-Dispatch, February 18, 2003, http://www.truthinjustice.org/mjburton.htm (accessed September 25, 2007).


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From The Police Chief, vol. 74, no. 11, November 2007. Copyright held by the International Association of Chiefs of Police, 515 North Washington Street, Alexandria, VA 22314 USA.








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