Courts and forensic evidence

SIGNIFICANCE: One of the most important reasons law-enforcement investigators gather evidence is to prove guilt in a court of law. The techniques used by forensic scientists must be acceptable to courts in order for the evidence obtained through those techniques to be admissible. Forensic scientists must thus be familiar with the types of evidence and the techniques used to gather and examine evidence that are most likely to be admissible in court.

Any evidence that has been gained through the application of scientific means can be considered forensic evidence. However, not all forensic evidence is considered legitimate; in the United States, federal, state, and military courts have had varied histories in regard to different types of forensic evidence. Many types of forensic techniques have not always been accepted, and the legitimacy of many continues to be debated.

Before evidence gathered through the use of a particular forensic technique can be considered admissible in a court of law, the technique must first be proven reliable. Most often, forensic techniques become accepted through common law, which is the practice of following prior decisions made in court. Any new forensic technique must be vetted by a judge; usually, this means that an attorney presents the technique in court and argues that the evidence produced using the technique should be admitted in a case.

For example, one of the first courts in the United States to accept the use of DNA (deoxyribonucleic acid) evidence was the Circuit Court in Orange County, Florida. In 1987, Assistant State Attorney Tim Berry successfully argued that the DNA from semen found on a murder victim matched DNA from a blood sample taken from the defendant, Tommy Lee Andrews, and that DNA comparison was a reliable method of establishing identity. To support his argument, Berry presented testimony by David Houseman, a research biologist from the Massachusetts Institute of Technology, and Michael Baird, a scientist at the laboratory where the samples where analyzed. Berry also compared the use of DNA matching to fingerprint identification, an already commonly accepted forensic method. In 1989, in the case of People v. Castro, the use of DNA for identification was seriously challenged in the New York Supreme Court. Over twelve weeks of testimony and arguments, the cases for and against DNA evidence were presented. In the end, the court found that DNA evidence is accepted by the scientific community and that DNA comparison is an accepted forensic technique. Since then, cases that use DNA evidence usually cite the case of People v. Castro to establish the admissibility of DNA evidence.

Admissibility of New Forensic Techniques

Before judges will accept evidence produced by new types of techniques, the evidence must first pass several tests. The first of these is the traditional relevance test. To pass this test, evidence must bring some fact to light and must not tend to confuse jurors more often than it enlightens them. Beyond that test, differences exist between the federal admissibility standard and the standard used by many state courts, the Frye standard, established in the case of Frye v. United States in 1923. The Frye standard’s “general acceptance” test requires merely that the techniques used to obtain or produce evidence must be generally accepted by the scientific community.

Federal courts, in contrast, as well as many state courts, follow a standard established by the US Supreme Court case of Daubert v. Merrell Dow Pharmaceuticals in 1993. The so-called Daubert standard has multiple parts: For evidence to be admissible, the technique used to obtain or produce it must be tested and peer-reviewed, the technique’s margin of error must be known and controlled, and the technique must be accepted within a relevant scientific community. The determination of whether these tests have been met is the responsibility of the trial judge. Since the Daubert decision, a great deal of debate has taken place concerning the role of judges as the “gatekeepers” of evidence. Many experts have lauded the decision as a way to keep pseudoscience out of the courtroom, whereas others have argued that Daubert gives judges too much individual discretion over what constitutes acceptable expert testimony.

Unlike fingerprint identification and DNA identification, some forensic techniques have not been accepted by US courts. In 1999, a Washington appeals court had to address an unusual new identification technique used by investigators in the case of State of Washington v. Kunze. An intruder who had killed two people in a house before robbing the house of most of its valuables had left a full impression of one of his ears on a wall in a hallway at the crime scene. An investigator from the Washington State Crime Laboratory was able to lift the ear print from the wall using a technique normally used for fingerprints. This print was compared with ear prints taken from the suspect, David Wayne Kunze, and a criminologist from the laboratory, Michael Grubb, concluded that the print from the wall was a likely match to the suspect. During pretrial hearings, however, Grubb admitted that he had never worked with ear prints for identification before and that he had not seen any studies about how often a particular ear shape might occur in the general population. Even though several other identification experts were called in, the prosecution could not establish that ear-print identification was generally accepted by the scientific community (the court in Washington followed the Frye test, not the Daubert test), and the court refused to accept ear-print identification as a legitimate forensic technique.

Some types of forensic evidence that were accepted by US courts for years have later been found to be unreliable. One forensic technique that has been discredited, comparative bullet-lead analysis (CBLA), was long practiced by the Federal Bureau of Investigation (FBI) and had been accepted by US courts since the 1960s. The technique involves comparing the composition of the metal in a bullet that was used in a crime with the composition of the metal in other bullets to establish the origins of the crime scene bullet. The technique is based on the idea that if the composition of two bullets is the same, then the bullets must have been made by the same manufacturer on the same day, using the same batch of material. This technique was used to produce the key evidence in a 1986 case against a man in North Carolina named Lee Wayne Hunt. He was convicted of two counts of murder and was in prison from 1986 until his death in 2019. However, in a 2004 report on a study requested by the FBI, the National Research Council of the National Academy of Sciences stated that CBLA is unreliable and can produce misleading results. Because of this, many cases such as the one against Hunt were under review.

Even forensic techniques that have come to be thoroughly accepted have not always been viewed as so reliable. In 1873, in the case of Tome v. Parkersburg Railroad Company, the court rejected photographic evidence because it said that photographs produced only “secondary impressions of the original” and that they were susceptible to changes in lighting. Only one year later, in the case of Udderzook v. Commonwealth, the Supreme Court of Pennsylvania found that photographs taken by an insurance company should be admitted as evidence. These photographs were used to prove that a body found in the woods was that of a particular man whom the insurance company had photographed when he took out his policy. The court wrote, “The [photographic] process has become one in general use, so common that we cannot refuse to take judicial cognizance of it as a proper means of producing correct likeness.” Since that day, attorneys have cited the case of Udderzook v. Commonwealth when presenting photographic evidence in court.

Federal, State, and Military Standards

Case law, also known as common law, is not the only source of determination for admissibility of evidence in court. In 1934, the US Congress passed the Rules Enabling Act, which gave the US Supreme Court the power to prescribe rules of practice and procedure and rules of evidence for the federal courts. Following this mandate, in 1965 Chief Justice Earl Warren appointed an advisory committee to write a comprehensive federal code of evidence. Over a ten-year period the committee debated, researched, drafted, heard public commentary, rewrote, and finally issued its code, the Federal Rules of Evidence (FRE). This code was debated in both houses of Congress and signed into law on January 2, 1975. The advisory committee was then disbanded and the rules were left unreviewed until 1992, when the Evidence Advisory Committee was re-created to oversee revisions to the FRE. Since that time, the committee has made few substantive changes to the code. The FRE is the codification of decades of precedence, and it is the core of admissibility standards in federal courts.

The FRE applies to all federal courts throughout the United States, but cases tried in state courts are subject to the states’ own individual standards of evidence. For the most part, states have followed the federal standards, but some, such as California, have separate sets of rules. Even in states that follow the federal standards, some important differences exist. For example, some states (including Connecticut, Massachusetts, and Texas) have followed the federal Daubert test, whereas others (including California, Florida, and New York) continued to apply the Frye test; still others (such as Delaware, Oregon, and Vermont) followed their own standards regarding the admissibility of forensic evidence. It is important for forensic scientists to understand the evidence standards that apply to their particular states.

In September 1980, the US military established its own separate rules of evidence to apply to courts-martial and other military courts. Although these rules were designed to follow the FRE closely, there were some noteworthy differences. One such difference stems from the 2005 Detainee Treatment Act, which says that military judges must, for statements made after the act was passed, determine whether the statements were obtained through cruel, inhuman, or degrading treatment before the statements can be considered as evidence. Some significant differences also exist between the FRE and military rules regarding hearsay, because witnesses in military trials are likely to be foreign nationals who are not amenable to the process.

The American legal system has had a difficult relationship with new forensic techniques because of the important role that forensic evidence can play. A case can turn on a single piece of evidence, such as the composition of the metal in a bullet, and the justice system must be careful in the decisions it makes about allowing particular evidence-gathering practices and the admissibility of specific kinds of expert testimony. If a process is not carefully vetted and established, then injustices are likely to occur.

Bibliography

Adam, Craig. Forensic Evidence in Court: Evaluation and Scientific Opinion. Wiley-Blackwell, 2016.

Best, Arthur. Evidence: Examples and Explanations. 10th ed., Wolters Kluwer, 2016.

Genge, N. E. The Forensic Casebook: The Science of Crime Scene Investigation. Ballantine, 2002.

Karagiozis, Michael Fitting, and Richard Sgaglio. Forensic Investigation Handbook: An Introduction to the Collection, Preservation, Analysis, and Presentation of Evidence. Charles C. Thomas, 2005.

Kiely, Terrence F. Forensic Evidence: Science and the Criminal Law. 2nd ed., CRC Press, 2006.

Levinson, Jay, Eti Buchnik, Barak Ariel, and Abraham J. Domb. "Scientific Evidence in Courts of Law: An Overview." In Judicial Independence: Cornerstone of Democracy. Shimon Shetreet and Hiram Chodosh, eds. Brill Nijhoff, 2024.

Lissitzyn, Christine Beck. Forensic Evidence in Court: A Case Study Approach. Carolina Academic Press, 2008.

Sapse, Danielle S. Legal Aspects of Forensics. Chelsea House, 2006.

Waggoner, Martha. "Confession Failed to Free Man Convicted in Fayetteville Murders, Who Has Died as a Prisoner." Fayetteville Observer, 10 Apr. 2019, www.fayobserver.com/story/news/crime/2019/04/10/confession-failed-to-free-man-convicted-in-fayetteville-murders-who-has-died-as-prisoner/5479351007/. Accessed 14 Aug. 2024.