Summoned by passersby to a murky canal in western New York State, homicide detectives discover a woman’s partial remains in a suitcase weighed down by a 20-pound bag of rice. Further investigation yields a block of concrete containing her head and a dumpster with still more body parts.

Steven Symes, Ph.D. analyzes saw marks on a
femur using a Leica MZ16A stereomicroscope
that allows for a magnified digital display with
maximum stereo resolution.

What type of weapon had been used to decapitate the victim, cut off her hands, and sever her remaining limbs? The answer could provide valuable clues as police endeavor to put a weapon to a killer, and, ultimately, as prosecutors assemble the evidence needed for a conviction.

Police place a call to forensic anthropologist Steven A. Symes, Ph.D., an authority on knife and saw mark analysis currently lending his expertise to a pioneering new master’s program in forensic and biological anthropology at Mercyhurst College in Erie, Pennsylvania. Symes can discern from the "signature" left on bone what class of sharp-bladed implement might have been used to accomplish a mutilation or dismemberment, be it a serrated knife, a garden-variety treesaw, or a lumberjack-grade chainsaw.

Powerful Evidence
Tool mark analysis has become a highly technical subfield of forensic science. Whether comparing the unique features of bullets, shoe prints, tire tracks, or the class characteristics of saw marks, the accuracy of diagnostic techniquesis vital to strengthening its validity as a legal instrument.

Yet, for all the advances in tool mark scrutiny, particularly in the field of firearms, Symes said few methodologies and no published standards exist for knife and saw mark analysis.

“At one end of the spectrum you have a significant number of cases involving dismemberment and mutilation and the potential for powerful evidence from reliable knife and saw mark analysis; at the other end you have a limited number of forensic practitioners involved in this type of analysis as well as a lack of adherence to Daubert criteria to support their conclusions,” Symes said. “The contradiction is glaring, and poses a growing need in the forensic community.”

Putting Teeth in Saw Mark Analysis
Now, with the support of the Applied Forensic Sciences Department at Mercyhurst College, distinguished colleagues, and funding from The National Institute of Justice,1Symes has undertaken research aimed at establishing a gold standard methodology for knife and saw mark analysis. The goal is to empower qualified forensic scientists to perform reliable analyses and support their conclusions with quantitative and statistical data. The National Forensic Academy andthe American Academy of Forensic Sciences are partners in the project.

Symes’ expertise dates back to 1987 when he began researching what would become a landmark doctoral dissertation on saw mark analysis of bone. Since then, he has provided analysis of cut marks in nearly 200 dismemberment cases and roughly 500 knife wound cases emanating from a wide range of local, state, and national investigative agencies. As a board member of the American Board of Forensic Anthropology, an exclusive group of fewer than 75 board-certified forensic anthropologists in North America, he has also applied bone trauma analysis to human rights investigations in Guatemala, El Salvador, Chile, Indonesia, Mexico, Peru, and Kosovo.

Because saw mark analysis has received little research attention in recent years, Symes maintains that many in law enforcement and forensic science remain unaware of the significant contribution the recognition, interpretation, and documentation of this type of sharp force trauma can add to the resolution of a case. It can narrow the search for a weapon; provide the link, or lack thereof, between a recovered weapon and the crime; and be of enormous evidentiary merit in a court of law.

Unfortunately, with many of these odious cases, valuable clues are often overlooked because many forensic practitioners do not care to include bone as a material within their realm of expertise. Further, organizations not able to sacrifice the time and money necessary for expert analysis are frequently forced to continue their investigations based on little evidence, or worse, inaccurate analysis. Even under expert analysis, the absence of published standards validated by the scientific community can make such evidence vulnerable to derision by defense lawyers as an interpretive art.

Misconceptions Impose Limitations
Historically, at least two major misconceptions contribute to the lack of accuratesaw mark analysis in the forensic sciences. When Symes began his original research two decades ago, conventional wisdom held that every pass of a saw on a bone erased the marks left behind by the previous stroke. But just as people leave fingerprints and firearms produce characteristic defects, he was convinced that blades leave telltale marks of their own.

So, he began by buying and borrowing every imaginable saw – rip saw, hack saw, circular saw, Japanese pull saw, and many more. Using donated arm and leg bones, he made thousands of experimental cuts, attempting pull strokes, false starts, rotary cuts, and others, while under the microscope he studied striations in the groove, or “kerf,” created by the sawing action. In time, he discovered that each saw class did indeed leave its own calling card.