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Some of what you see on the popular crime scene investigation TV dramas is an accurate reflection of real world investigations. Most of what you see is somewhere between questionable and downright laughable. The objective of the real world investigators is to examine all aspects of the criminal incident, the place(s) where the crime occurred, as well as the people involved. A broad range of evidence items are collected, packaged, and delivered to the crime lab.

Ample communication between the investigators and the crime lab analysts assigns a level of priority for the examination of each item. The crime labs are populated with individuals possessing a variety of specialized skills and technological tools. A brief-but extremely informative- INTERVIEW WITH DR. RICHARD SAFERSTEIN illuminates the basics of crime scene analysis and dissects how evidence is supposed to be processed through the crime labs.

It is noteworthy that—for twenty-one years—Dr. Saferstein headed one of the largest forensic laboratories in the U.S., the New Jersey State Police Crime Lab. Although he is now retired, the man served as a forensic expert witness associated with over 2000 proceedings in nearly 150 federal and state courts. Dr. Saferstein literally wrote THE BOOK on forensic science. Criminalistics: An Introduction to Forensic Science, is currently in its ninth edition. In 2006, Dr. Saferstein received the American Academy of Forensic Sciences Paul L. Kirk Award for distinguished service and contributions to the field of Criminalistics.

FORENSIC SCIENCE DISCIPLINES used at the crime labs can include analysis of the following: DNA, blood spatter patterns, trace materials, latent prints, footprints, tire prints, drugs, ballistics, tool marks, forensic anthropology, forensic entomology, digital/computer forensics, and handwriting/document examinations.

This article--and the vast majority of content on this blog--will focus on DNA. Biological material detected on evidence items can lead to the characterization of useful DNA profiles. For any criminal case, DNA technology offers the potential to emerge as a dazzling investigative game changer. With that said, ...and as powerful as genetic technology truly is, there is never a guarantee that useful DNA results will be found on any of the evidence collected from a given crime scene. In fact, investigations that uncover significant DNA data are clearly outnumbered by the many cases in which the technology never becomes a factor.

The biggest disparity between real life criminal cases and the CSI dramas boils down to realistic versus unrealistic investigative instincts. The TV actors portraying CSIs somehow possess a MIRACULOUS knack for looking precisely where they need to—without fail—in every single episode. In real life, the investigators and forensic biologists may have respectable intuitive abilities. However, if every law enforcement professional possessed superhuman psychic powers, DNA-based exonerations would never be necessary and would never happen. According to the INNOCENCE PROJECT WEBSITE, as of the end of 2011, 301 wrongfully accused individuals have been set free as a consequence of DNA testing. Although I occasionally tune in to the Investigation Discovery Channel for 48 Hours, Dateline, or On the Case With Paula Zahn, I rarely find myself pausing briefly on one of the CSI dramas. Can any of my readers please let me know if these fictional programs have ever mentioned the alarming inventory of wrongful convictions that continue to be reversed by DNA?

Let us put aside the many criminal cases that do not involve any notable DNA results. Let us also consider that *sometimes* the biological/DNA evidence clearly identifies a wretched perpetrator-who is justifiably whisked away to prison by the irresistible force of DNA typing evidence—and perhaps a mountain of other, supporting facts that establish their guilt.

What remains is a small percentage of investigative cases trickling into our criminal justice system. This article is centering on those cases involving biological/DNA testing, with results available to both the prosecution and the defense, but with conspicuous or subtle ambiguities residing within the scientific data. These ambiguities can lead to baffling misinterpretations and fierce controversies playing out in our courtrooms. As small as this percentage of cases might be, consider this: Approximately 2.2 to 2.5 million Americans are currently incarcerated in our jails and prisons. If only one out of every 100 of these cases involves disputable biological/DNA interpretations, this translates into 20,000 problematic cases.

At this point, some readers might decide to shout from their rooftops, “But wait a minute! The CSI dramas have taught us that DNA evidence is infallible!” Wrong. DNA IS JUST AS PRONE TO FALLIBILITY as any of the other forensic disciplines. Perhaps our most devout CSI fans are asking, “Explain these problematic issues confronting DNA cases within our criminal justice system?” I am glad you asked.

In order to dissect these issues, we must first establish the basics of how a forensic science lab proceeds after the biological evidence is delivered by law enforcement officers. First, it is crucial to note that the individuals delivering the evidence are indeed LAW ENFORCEMENT OFFICERS. In contrast, the analysts receiving the evidence at the crime lab are SCIENTISTS. This raises an enormously important initial question: Are the scientists-who are about to scrutinize the DNA evidence-part of the law enforcement structure? Perhaps these scientists consider themselves independent of the law enforcement/prosecution team. Do the CSI dramas depict forensic biologists as sensitive souls, toiling away in the lab for the purpose of protecting the rights of the accused? If you embrace the latter option, ….please stop kidding yourself and consider watching more episodes of CSI. The scientists work for the police.

Over the course of four years, May 2003 through May 2007, I worked over 100 cases as a forensic biologist for the Indiana State Police-Evansville Regional Crime Laboratory. I considered myself an employee of the taxpaying victims of crime, and their families. My role was to serve the criminal justice system, and assist with identifying the true perpetrators of the crimes. I made countless friends with people working in law enforcement. While my scientific data-and my subsequent interpretations DID often support their causes, I was not working strictly for the police.

The first step in forensic biological evidence analysis is to lay out each item, one by one, and examine the items for biological material. The item can be virtually ANYTHING-an article of clothing, an empty soda can, a cotton swab from an apparent drop of blood, a knife, a toothbrush, a pillow case, etc. On more than one occasion, I opened up my brown paper evidence bag, only to find that an investigator was presenting me with, …the contents of a trash container. Forrest Gump’s assessment of a box of chocolates comes to mind.

After an initial round of scrutiny, spreading, sorting, under the ambient lights of the lab, items are often examined with a sophisticated ALTERNATE LIGHT SOURCE. These amazing instruments assist biological examinations by utilizing a multitude of light wavelengths. The forensic biologist is typically looking for clues pointing to the presence of blood, saliva, or semen. If any of these fluids is suspected to be present, there are a variety of universally accepted presumptive or confirmatory tests to detect them. The ultimate goal is to find sources of DNA.

On any given item, a scientist might expect to find trace amounts of DNA (guns, knives, tools, cotton swabs from door knobs, windows, steering wheels, etc.), wearer DNA (clothing). Epithelial cells/skin cells have a tendency to slough off of human beings at a steady rate, and attach themselves to a variety of surfaces.

Once the sources of biological material are presumed to be found-the forensic biologist extracts and ‘cleans up’ the DNA from these sources. The amount of extracted DNA can be estimated by utilizing a sophisticated machine, called a Real-time PCR instrument. Real-time PCR technology can estimate the recovery of incredibly small quantities of DNA—well beyond ONE BILLIONTH OF A GRAM. If you are not a big fan of the metric system, go make yourself a cup of tea. A typical packet of artificial sweetener contains one gram of material. One billionth of that packet is a nanogram, ….which is invisible to the human eye.

When a forensic biologist introduces a DNA sample into the DNA typing system, he/she might load in, let us say 10 billionths of a gram (this is 10 nanograms). The DNA typing results would most likely provide a mess-TOO MUCH DNA! Only a nanogram or two is needed for the DNA typing process to work optimally. If a forensic biologist determines that only ¼ of a nanogram is available for the DNA typing process, it would not be a surprise to get a complete DNA profile anyway. The sensitivity of DNA typing is truly astonishing.

Allow me to pause here and encourage readers to skim through my various POWERPOINT PRESENTATIONS—which can illuminate DNA technology/criminal cases, DNA testimony, DNA transfer events, and other topics. Thus far-I have tried to avoid burdening my readers with the technical details of precisely HOW a forensic biologist determines a DNA profile from as little as one nanogram of DNA. This process is called “STR typing”, and it utilizes what is referred to as “PCR”. STR is an acronym for Short Tandem Repeats. PCR is an acronym for Polymerase Chain Reactions. It is important for a DNA expert to avoid belaboring an explanation of such acronyms to juries and overwhelming them with too much scientific jargon. If you catch me doing that, I apologize—please let me know.

The following information demonstrates how I avoid these pitfalls, as I help juries to visualize the basics of how the complicated STR-based DNA typing process is accomplished:

Individuals receive half of their DNA from their mom and half from their dad. With few exceptions, siblings will have very similar DNA, whereas identical twins will have the exact same DNA profile. The vast majority of cells in your body will have a full complement of your DNA-and this DNA will be identical from cell type to cell type, from head to toe. Your DNA is composed of long chains of building blocks, ….billions of them. Think of your genetic material as a huge book of information, ….a book so large, it would dwarf War and Peace

Just a couple of decades ago, human genome scientists and forensic scientists put their heads together to develop a DNA-based identification system. The scientists knew that it would be impractical to have crime labs sift through billions of building blocks of information from each crime scene sample. The analyst would essentially have to sit down and read War and Peace—for each sample! As this would cause nervous breakdowns and bankrupt the crime labs, the scientists managed to unveil certain ‘identifier pages’ within the huge genetic book of DNA. These few pages showed significantly different information from one individual to the next. Once these pages were revealed, a process (PCR) was developed to capitalize on the discovery.

The PCR process can be visualized by jurors as a “molecular photocopier”. PCR targets only these identifier pages of the book and makes numerous copies of each page. Specifically, fourteen separate pages became the main focus of this human identification project. Each page is a genetic location—called a ‘locus’. One of the fourteen loci tells us ONLY the gender of the person being typed. Cumulative information from the remaining thirteen specific loci, demonstrates a genetic pattern that serves as a unique identifier for a each person (except for identical twins). In 1993, Kary B. Mullis was awarded the NOBEL PRIZE IN CHEMISTRY, for developing the PCR process that made all of this possible.

With PCR technology, the forensic biologist can take—for example—a tiny, isolated speck of blood from a crime scene, extract the DNA, quantify the DNA, and rapidly determine the STR typing data. The scientist can subsequently collect known standard DNA typing data from a suspect, an alleged victim, witnesses, etc., and *hopefully* determine the contributor of this blood speck at the crime scene. It is important to note that the DNA typing process CANNOT tell us WHEN the DNA came to be on the evidence, or HOW it came to be on the evidence.

Calculations can be made—by the crime lab—to establish the statistical probability of finding a given STR typing profile within random individuals among the human population. When a full DNA profile is determined, from a single individual on an evidence item, and it is a perfect, locus-by-locus match to a known individual, it would not be unusual to estimate that 1 out of every quintillion humans (1 out of 1,000,000,000,000,000,000) are expected have that DNA type. This number is over 140 million times larger than the entire population of the earth. Such data are compelling to juries.

Once again, my readers might be jogging back to their rooftops and shouting, “CSI must be right after all. How can 1 out of every 1,000,000,000,000,000,000 be infallible?” The astonishing sensitivity of forensic DNA typing (detection of mere fractions of nanograms) and the dazzling discriminating power of forensic DNA (probability of inclusion statistics reaching the quadrillions, quintillions, sextillions of human beings?) is NOT where these processes are fallible. Fallibility enters the equation when human beings are asked to scour the crime scenes, collect the evidence, examine the items, and interpret the biological/DNA data. Human errors and misrepresentations of the facts associated with these tasks are the points of origin that can ultimately lead to wrongful convictions.

The role of DNA technology in our criminal justice system can go terribly wrong in many ways. Examples of these troubling circumstances can include, but are not limited to the following:
  • DETECTION OF DNA MIXTURES, sometimes originating from multiple, unknown individuals.
  • A partial DNA profile is observed-with the DNA potentially originating from a variety of related, genetically similar individuals.
  • Profoundly small quantities of DNA are recovered from items that either were not—or could not—be assessed for the presence of saliva, blood, or semen. In such cases, the collection of substrate controls can have a profound impact on the DNA results.
  • In addition to failing to collect substrate controls from a crime scene, it is possible for the CSI to overlook that one VITAL piece of biological evidence that would have identified the actual perpetrator of a crime.
  • Perhaps that one vital evidence item IS collected, but is kept in storage, overlooked by the forensic biologist, and never examined for body fluids or DNA.
  • Misinterpretation of presumptive body fluid tests as confirmatory proof that the body fluid is present. The FBI Crime Lab was at the center of an EXAMPLE OF SUCH A CASE.
  • Forensic DNA typing can be misrepresented to juries when the crime lab analyst is allowed to speculate as to HOW or WHEN DNA became associated with an evidence item. For example, referring to a trace amount of DNA as “touch DNA” when there is no evidence that the item was ever directly handled by the individual with the matching DNA profile.
  • Forensic DNA typing results can be misrepresented to juries when the crime lab analyst is allowed to testify and discuss sub-threshold signals detected on DNA typing electropherograms-contradicting the fact that the crime lab guidelines clearly warn that these signals may be procedural artifacts-rather than actual DNA.
  • Contamination of crime scene evidence with DNA sources that are unrelated to the criminal investigation. EXAMPLE OF THIS.
  • Important note: In many instances, collection and testing of substrate controls at the crime scene is a valuable consideration. Such scientific controls can provide experimental safeguards illuminating the MECHANISMS by which DNA might have arrived at a specific location. For more information on the utility of substrate controls, refer to the INTERVIEW WITH DR. RICHARD SAFERSTEIN.
This article has only begun to scratch the surface of why we—as a society—must carefully monitor the dynamic role of DNA technology in our criminal justice system. Future articles will summarize specific examples corresponding to the bullet list provided above.

The next article will be entitled: Why Defense Counsel Might Need A DNA Expert

Michael J. Spence, Ph.D.


December 27, 2011


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