trying to solve a math problem with only half the numbers?” You’re mostly right, but the expert can’t change but rather must work within the law. She can present only the information the court allows and must explain it as fully as possible in a true and unbiased opinion. Doing so helps the jury get as close to the truth as possible.
Understanding the role of expert testimony
Judges typically allow a great deal of leeway with regard to how expert witnesses present information to the jury. Most witnesses are permitted only to answer questions. If they attempt to move too far afield of the question, the judge will rein them in. Experts, on the other hand, are allowed to depart from the normal Q-and-A format because their often-technical testimony necessitates explanation. Indeed, the expert teaches the judge and jury. For example, understanding the impact of DNA evidence is difficult for the average juror when presented simply from a series of questions with yes or no answers. Enabling the expert to explain what DNA is, how it is tested, and what the results of the testing mean gives the jurors the knowledge they need to understand and evaluate the evidence.
Regardless of who presents the information, by virtue of Frye v. United States, judges require that the science behind the evidence be real and not junk science coming from someone merely spouting personal beliefs without any scientific support.
In 1923, the District of Columbia Circuit Court addressed whether the results of a polygraph examination (lie detector test) were admissible as evidence in that case. The landmark decision in Frye v. United States set what later became known as the Frye Standard for presenting scientific evidence before the courts. The standard states that the court can accept expert testimony on “well-recognized scientific principle and discovery,” if it is “sufficiently established” and has achieved “general acceptance” in the scientific community. This acceptance enables new scientific tests to be presented, but only after they’ve been thoroughly hashed out and accepted.
Although Frye was the standard for many years, and still is followed in many jurisdictions, it more recently was replaced by Daubert v. Merrell Dow Pharmaceutical, Inc., or Rule 702 of the Federal Rules of evidence, which states that judges may use their discretion to admit expert testimony to “understand the evidence” and to “determine a fact in issue.” Rule 702 was upheld and amplified in 1993 by the United States Supreme Court, which held that the “general acceptance” clause in Frye was not absolute, thus handing judges wider discretion as to what expert testimony they can allow in any given case. To further help judges, the court offered several guidelines. For a new scientific technique or theory to be acceptable to the court, it must
✔ Be subject to testing and to peer review
✔ Be standardized with recognized maintenance of such standards
✔ Have a known and accepted error rate
✔ Attain widespread acceptance
The high court’s ruling basically means that the technique or theory must be spelled out, tested, reviewed, accepted, and continually monitored for accuracy.
Whether scientific evidence and testimony are admissible often is hammered out by attorneys and the judge in pretrial hearings and motions that the jury never hears. If the evidence to be presented by the expert passes the Frye or Daubert standards, the judge allows the jury to hear the expert testimony. If not, the judge may exclude it from the trial.
Chapter 3
Collecting and Protecting the Evidence
In This Chapter
▶ Checking out the crime scene
▶ Identifying types of evidence
▶ Obtaining a search warrant
▶ Gathering and preserving evidence
▶ Figuring out where the body went
Crime scenes are like puzzles and, when investigators are lucky, the pieces fit neatly together. In other cases, determining what happened is like trying to create a picture from two or three different puzzles where you have plenty of pieces, but they don’t fit. And investigators often have to deal with pieces that just aren’t there.
Because solving a crime and convicting a perpetrator depend upon evidence, investigators take a methodical approach to finding and handling evidence at crime scenes. They work hard to protect the evidence and to leave nothing important behind. Throughout the process, investigators formulate theories about what happened. If they do their jobs well, they end up with a complete picture of the crime. In this chapter, I fill you in on exactly how investigators deal with evidence and crime scenes.
From the moment the first police officer arrives at the scene, he follows a strict set of procedural guidelines designed to protect him and everyone else who’s present; guard evidence against damage, contamination, or loss; and document everything that occurs at the scene. Following these procedures and maintaining control of the scene until the crime-scene investigators arrive offer the best chance of getting the evidence needed to identify and convict the perpetrator. Failure to follow these directives can result in the crime remaining unsolved or a known perpetrator walking free.
Distinguishing between primary and secondary crime scenes
There may be more to a crime scene than first meets the eye. In fact, more than one crime scene may exist, depending upon how the crime was committed, not to mention where. Crime scenes, therefore, are considered either primary or secondary. The primary crime scene is where a crime actually occurred. A secondary crime scene is in some way related to the crime but is not where the actual crime took place.
Primary scenes typically yield more usable evidence than do secondary scenes, but not always. Sometimes the only crime scene investigators have to work with is a secondary scene, such as the place where a serial killer dumps a victim’s body, for example. Under these circumstances, investigators may not know where the actual murder took place and therefore use evidence they find at the secondary scenes to help them identify the killer or locate the primary scene. They may be able to use fibers from an expensive or unusual carpet they found on the victim to identify the manufacturer, the seller, and ultimately a list of buyers or locations where that
