Forensics For Dummies. Douglas P. Lyle

The goal is to make each scientific procedure reliable, reproducible, and uniform in every crime lab across the country as well as to establish standards and qualifications for experts in each area of forensic science. It’s a tall order and will take time, but these organizations, and the working groups and committees they have established, are moving in the right direction.

      Added to this is the problem of examiner bias, laziness, and corruption. Many cases of “experts” falsifying or “dry labbing” the evidence have cropped up in recent years. Dry labbing simply means coming up with results without actually doing the testing. We have seen this with DNA, fingerprints, bite marks, and other forensic techniques. Part of the work of the organizations previously mentioned is to identify and remove such individuals from the scientific community.

      What does this mean for the current state of forensic science? Simply that the quality of the evidence uncovered and the expertise and honesty of the examiners is critical to the reliability of the results, and any move to improve that is a positive change. For example, if a good-quality fingerprint is found at a crime scene and it is examined and compared by a qualified expert, the results are very reliable. Even though no true scientific evaluation of fingerprint techniques has been done, the facts are that despite countless millions of fingerprints being obtained around the world, no two have ever been shown to be identical. Even identical twins have different fingerprints. So forensic science is sound; it simply needs to be standardized and uniformly applied.

       Understanding the court system

      The court system in the United States is adversarial by nature, meaning that each side attempts to outfox or outargue the other. The prosecutor and defense attorney attempt to present evidence that favors their respective side and spin any contrary evidence in a manner that supports their theory regarding the case. This locking of horns can put the forensic expert in a difficult position. Each side is likely to bring in outside experts to support or refute the testimony of the ME. These experts may even be other forensic pathologists, toxicologists, firearms experts, or someone from any of the other forensic areas.

      Each expert can expect to be qualified before the jury, meaning that the opposing attorneys ask questions about the expert’s credentials, training, experience, areas of expertise, teaching positions, publications in the field in question, and anything else they think will support or undermine the expert’s true qualifications. In general, the side that calls on an expert as a witness asks easy, supportive questions, and the opposing side asks tougher questions aimed at impeaching, or refuting, the qualifications and any testimony the expert gives. Expert witnesses must be prepared for potentially unsettling questions.

      Experts presenting testimony need to be honest and measured, trying not to oversell their points of view, but making their honest opinions clear, concise, and believable. That is, experts must appear neither too sure nor too unsure of their opinions. The former may alienate a jury, and the latter may undermine the expert’s credibility.

       Getting to the heart of the “truth”

      The real goal of court proceedings is not so much to uncover the absolute truth as it is to provide enough evidence so a jury can reach an understandable version of the truth based on the applicable rules of law. Getting to that version is complicated by the fact that certain items of evidence may not be admissible (allowed into the courtroom at the time of trial) in court, because they were obtained improperly, contaminated, or overly inflammatory or prejudicial.

      So, you may be wondering: “If some evidence is excluded, how can the absolute truth be found? Isn’t that like 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.

      

Rarely will an expert witness express testimony as an absolute fact, especially when being challenged by the other side. Instead, the wise expert uses phrases such as “similar to,” “consistent with,” “not dissimilar from,” “compatible with,” or “shares many characteristics with.” Why is this? The truth is that forensic evidence rarely, if ever, is absolute but rather states probabilities. For example, except for identical twins, no two people have the same DNA, but the testifying expert should never say the DNA “absolutely matches” that of the defendant. Instead, the expert should say that the probability that it matches someone other than the suspect is a billion to one. That is almost, but not quite, absolute.

Holding testimony to standards of acceptance

      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