What is LawBrain?
It's a living legal community making laws accessible and interactive. Click Here to get Started »

DNA Evidence

From lawbrain.com

Among the many new tools that science has provided for the analysis of forensic evidence is the powerful and controversial analysis of deoxyribonucleic acid, or DNA, the material that makes up the genetic code of most organisms. DNA analysis, also called DNA typing or DNA profiling, examines DNA found in physical evidence such as blood, hair, and semen, and determines whether it can be matched to DNA taken from specific individuals. DNA analysis has become a common form of evidence in criminal trials. It is also used in civil litigation, particularly in cases involving the determination of paternity or identity.


History and Process of DNA Analysis

DNA, sometimes called the building block or genetic blueprint of life, was first described by the scientists Francis H. C. Crick and James D. Watson in 1953. Crick and Watson identified the double-helix structure of DNA, which resembles a twisted ladder, and established the role of DNA as the material that makes up the genetic code of living organisms. The pattern of the compounds that constitute the DNA of an individual life-form determines the development of that life-form. DNA is the same in every cell throughout an individual's body, whether it is a skin cell, sperm cell, or blood cell. With the exception of identical twins, no two individuals have the same DNA blueprint.

DNA analysis was first proposed in 1985 by the English scientist Alec J. Jeffreys. By the late 1980s, it was being performed by law enforcement agencies, including the federal bureau of investigation (FBI), and by commercial laboratories. It consists of comparing selected segments of DNA molecules from different individuals. Because a DNA molecule is made up of billions of segments, only a small proportion of an individual's entire genetic code is analyzed.

In DNA analysis for a criminal investigation, using highly sophisticated scientific equipment, first a DNA molecule from the suspect is disassembled, and selected segments are isolated and measured. Then the suspect's DNA profile is compared with one derived from a sample of physical evidence to see whether the two match. If a conclusive nonmatch occurs, the suspect may be eliminated from consideration. If a match occurs, a statistical analysis is performed to determine the probability that the sample of physical evidence came from another person with the same DNA profile as the suspect's. Juries use this statistical result in determining whether a suspect is guilty or innocent.

Although DNA analysis is sometimes called DNA fingerprinting, this term is a misnomer. Because the entire DNA structure of billions of compounds cannot be evaluated in the same way that an entire fingerprint can, a "match" resulting from DNA typing represents only a statistical likelihood. Thus, the results of DNA typing are not considered absolute proof of identity. A DNA nonmatch is considered conclusive, however, because any variation in DNA structure means that the DNA samples have been drawn from different sources.

An example from the early 1990s illustrates the way in which DNA evidence is used in the criminal justice system. After a Vermont woman was kidnapped and raped in a semi-trailer truck, police identified Randolph Jakobetz, a truck driver, as a suspect in the crime. Officers searched the trailer that Jakobetz had hauled on the night of the crime and found hairs matching those of the victim. After arresting Jakobetz, law enforcement officials sent a sample of his blood to the FBI laboratory in Washington, D.C., for DNA analysis and for comparison with DNA taken from semen found in the victim shortly after the crime.

At Jakobetz's trial, an FBI expert testified that the blood and semen samples were a "match," concluding that there was one chance in 300 million that the semen samples could have come from someone other than Jakobetz. Based on this and other strong evidence, Jakobetz was convicted and sentenced to almost 30 years in prison.

Jakobetz appealed the decision, claiming that DNA profiling was unreliable and that it should not be admitted as evidence. In the first major federal decision on DNA profiling, the U.S. Court of Appeals for the Second Circuit upheld the lower court's decision to admit the DNA evidence (United States v. Jakobetz, 955 F.2d 786 [2d Cir. 1992]). The U.S. Supreme Court later declined to hear an appeal.

The Jakobetz case illustrates the way in which the probabilities generated by DNA analysis can be used as devastating evidence against a criminal suspect. Juries have tended to view the statistical results of this analysis as highly incriminating, which has caused many defense attorneys to challenge the validity of the results, and many prosecuting attorneys to defend them. At the same time, defense lawyers have used DNA analysis as evidence to reverse the convictions of their clients.

Legal History of DNA Evidence

In general, state and federal courts have increasingly accepted DNA evidence as admissible. The first state appellate court decision to uphold the admission of DNA evidence was in 1988 (Andrews v. Florida, 533 So. 2d 841 [Fla. App.]), and the first major federal court decision to uphold its admission occurred in Jakobetz. By the mid-1990s, most states' courts admitted DNA test results into evidence.

No court has rejected DNA evidence on the grounds that the underlying scientific theory is invalid. However, some courts have excluded it from evidence because of problems with the possible contamination of samples, questions surrounding the significance of its statistical probabilities, and laboratory errors. Several states have passed laws that recognize DNA evidence as admissible in criminal cases, and others have enacted laws that specifically admit DNA evidence to help resolve civil paternity cases.

The admissibility of novel scientific evidence such as DNA profiling is governed by two different judicial tests or standards: the Frye, or general acceptance, standard, and the Daubert, or relevancy-reliability, standard. The Frye test, which comes from the 1923 case Frye v. United States 293 F. 1013 (D.C. Cir.), holds that the admissibility of evidence gathered by a specific technique (such as DNA analysis) is determined by whether that technique has been "sufficiently established to have gained general acceptance in the particular field in which it belongs." In Frye, the Court of Appeals for the District of Columbia Circuit ruled that a lie-detector test using a blood-pressure reading was not admissible as evidence. By the 1970s, 45 states had adopted this common-law standard for the admission of novel scientific evidence.

The U.S. Supreme Court overruled use of the Frye test in federal courts in its 1993 decision Daubert v. Merrell Dow, 509 U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469. In Daubert, the Court held that the federal rules of evidence, enacted in 1975, govern the admission of novel scientific evidence in federal courts. It found that Frye provides too stringent a test and that it is incompatible with the federal rules, which allow the admission of all evidence that has "any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence" (Fed. R. Evid. 401). The Court found that judges have a responsibility to "ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable."

In general, courts that have used the Daubert standard have been more likely to admit DNA evidence, although many jurisdictions that have relied on Frye have permitted it as well. Nearly all cases in which DNA evidence has been ruled inadmissible have been in jurisdictions that have used Frye.

States are free to adopt their own standards for the admission of evidence, and have increasingly adopted the Daubert standard. By 1995, the number of states using the Frye standard had dropped to 23, while 21 had adopted the Daubert standard.

Current Issues Surrounding Use of DNA Evidence

A report issued by the Justice Department in 2002 indicated that two-thirds of chief prosecutors in the United States rely on DNA testing during investigations and trials. The use of DNA evidence has exonerated at least ten individuals who were wrongly convicted of murder and faced the death penalty, while the sentences of more than 100 others convicted of lesser crimes were overturned based upon DNA evidence. The FBI maintains a database that may be used to compare DNA samples from unsolved state and federal crimes. Since its inception in 1992, the FBI's database has made more than 5,000 matches, thus allowing law enforcement officials to solve crimes that might not have been solved without the use of DNA.

The FBI crime laboratory dominated research in forensic sciences for much of the 1980s and 1990s. However, allegations surfaced in 1995 that suggested scientists at the crime lab had tainted evidence related to the 1993 bombing of the World Trade Center in New York City. A former chemist in the lab, Frederic White-hurst, testified before the House Committee on the Judiciary that the FBI had knowingly drafted misleading scientific reports and pressured FBI scientists to commit perjury by backing up the false reports. These allegations injured the FBI's reputation and led to speculation in the late 1990s that prosecutors could not rely on the FBI's analysis of DNA evidence.

Even as the FBI rebuilt its reputation, other questions surrounding the use of DNA evidence have arisen since the late 1990s. In 1999, the department of justice issued a report stating that evidence from at least 180,000 unsolved rape cases had not been submitted for testing. A 2002 report by USA Today suggested that several thousand pieces of evidence from rape and homicide cases had not been submitted for DNA testing, so they do not appear in the FBI's database. In 2000, Congress allocated $125 million to support the national DNA database system, including $45 million designated to allow states to test evidence from unsolved crimes. However, several states claim that their law enforcement officials are so swamped with current cases that they cannot test older, unsolved cases. Moreover, a small number of states—primarily New York, Florida, Virginia, and Illinois—have aggressively developed their own DNA databases and have contributed heavily to the FBI's system. These states accounted for more than half of the FBI's DNA matches between 1992 and 2002.

Use of DNA evidence to overturn criminal convictions remains a common topic of discussion among legal and criminal justice experts, as well as the popular media. One of the most closely followed cases involved the convictions of five young men for the rape of a jogger in Central Park in New York City in 1989. The five men in the case, dubbed the "Central Park Jogger Case," served sentences ranging from seven to eleven years for the incident. However, another man, Matias Reyes, who was convicted for murder in 1989, confessed to the rape. Testing confirmed that the semen found in the victim and on the victim's sock matched Reyes's DNA.

Upon receiving the new evidence, the New York County district attorney's office asked the New York State Supreme Court to overturn the convictions of the five men. Several groups, including women's rights groups, cited this case as an example of why law enforcement should be more proactive in pursuing unsolved rape cases through the use of DNA testing.

Further Readings

Bennett, Margann. 1995. "Admissibility Issues of Forensic DNA Evidence." University of Kansas Law Review 44 (November).

"Confronting the New Challenges of Scientific Evidence: DNA Evidence and the Criminal Defense." 1995. Harvard Law Review 108 (May).

Federal Bureau of Investigation. 1994. Handbook of Forensic Science. Washington, D.C.: U.S. Government Printing Office.

National Research Council. 1992. DNA Technology in Forensic Science. Washington, D.C.: National Academy Press.

Wright, Eric E. 1995. "DNA Evidence: Where We've Been, Where We Are, and Where We Are Going." Maine Bar Journal 10 (July).

See Also