INTRODUCTION

• Jurisdiction: United States

Introduction

This textbook is designed to examine the process by which forensic evidence is used in the court system through case studies and the case law that has resulted when forensic evidence has been introduced. The text is designed for any student of law, criminal justice, or political science who wishes to understand both the power and the limitations of forensic evidence. The primary focus will be on criminal trials, in which forensic evidence is frequently introduced to prove one of two critical issues: (1) is the defendant the perpetrator of the crime, or (2) what happened at the crime scene?

As you will see, forensic evidence is frequently more reliable in excluding a defendant as the perpetrator (for example, the fingerprint on the weapon is not the defendant's or the blood at the scene is not the defendant's) than in positively identifying the defendant (for example, the hair sample or shoeprint at the scene is "consistent with" a class of individuals that includes the defendant but also many other individuals).

You will also learn how the rules of the U.S. court system limit the ways forensic evidence may be introduced in a trial, the types of expert "opinions" that may be offered in evidence, and the limitations on the ability of an appellate court to use its own judgment in deciding whether forensic evidence should have been introduced or excluded.

The public fascination with forensic evidence was captured with the advent of DNA testing. DNA evidence was introduced in 1995 in the trial of O.J. Simpson, in which a jury failed to convict Simpson of the murder of his wife, Nicole, and Ron Goldman, a waiter, despite a mass of DNA evidence pointing to his guilt. Due in part to the introduction of evidence that some DNA evidence may have been deliberately planted and testimony about a racist detective, the jury concluded there was "reasonable doubt" about Simpson's guilt. A different jury, in a subsequent civil trial, on virtually the same evidence, found based on a "preponderance of the evidence" that Simpson was liable in monetary damages for killing Nicole and Ron Goldman. This may be due in part to the fact that the standard of proof that a criminal jury uses requires a higher level of proof than that of a civil jury.

Television shows such as CSI depict detectives processing forensic evidence and getting a "hit" on a suspect. In most jurisdictions, the personnel who process forensic evidence hold degrees in chemistry or other scientific studies and work separately from the police force. Several types of forensic evidence, such as DNA and fingerprints, are either processed by commercial laboratories, as in the case of DNA, or are processed in part by computer systems that yield reports that must be read and evaluated by a fingerprint expert before a "match" can be declared. DNA, in particular, is almost never processed overnight and the DNA backlogs in many states have led to substantial questions about the justice system's ability to render a speedy verdict.

However, juries may expect forensic evidence and this expectation, sometimes called the "CSI effect" may present problems at trial, similar to earlier tendencies of juries to simply accept as fact the opinion of an expert witness due to the "White Coat Effect." Today juries are sophisticated enough to realize that both the prosecution and the defense pay for their expert witnesses, who often give conflicting reports. However, many defendants who rely on public defenders may not be able to afford to pay an expert witness, which presents another access to justice issue.

In 1993, the use of forensic evidence in court was radically changed by the U.S. Supreme Court in a civil case involving whether a drug caused birth defects. This case, Daubert v. Merrell Dow Pharmaceuticals,¹ stated that in deciding whether to admit scientific testimony under the Federal Rules of Evidence, the party proposing to offer the evidence must show that it meets certain tests that demonstrate that it is based on the scientific method, tested, and reliable. This test subsequently was incorporated into a revised federal rule of evidence and subsequently adopted in most state rules of evidence. Therefore, it applies in almost all federal and state criminal cases today. This inquiry often requires attorneys and judges to understand the scientific method and statistics, which many do not.

Although Daubert was a civil case, the language of the Supreme Court opinion applies to any case — civil or criminal—in which forensic evidence is proffered. And it set off thousands of subsequent court hearings on admissibility and appeals based on convictions where the defendant contended that the evidence either should or should not have been admitted under the Daubert standard.

One important issue we will examine is the Supreme Court's "alternate test" that scientific evidence can also be admitted if it is "generally accepted" in the scientific community. This has led to a dispute over defining the scientific community. Is it composed of academics or law enforcement? Another dispute is whether "generally accepted" is the same...