The Body as Evidence

  

 Although all humans are of the same species, with the same overall body parts, there are a number of attributes that are specific to each individual, even in the case of identical twins. These specifics come in handy when it comes to solving crimes.

During grad school, I had the good fortune of completing a Directed Independent Study at the C.A. Pound Human Identification Lab, located on the outskirts of the University of Florida campus. I trained under the assistant director, Dr. Michael Warren, who would go on to play a leading forensic role in the infamous Casey Anthony trial. The training was meant to supplement my studies in bioarchaeology, for both forensic anthropology and bioarchaeology utilize many of the same techniques. Both specialties rely on the examination of the skeleton; however, bioarchaeology deals with ancient remains while forensics focuses on contemporary deaths – typically those occurring within the past fifty years.

Working at the Pound Lab was a great experience. Each day, Michael would pull a box from the back shelves where the old cases reside and I would set to work on the remains, placing the bones in anatomical order, determining the age, sex, and height of the person, and noting any pathologies and unique identifiers, such as dental work or skeletal anomalies. From X-raying decapitated heads to defleshing a young girl, my work at the lab provided an up-close-and-personal glimpse of forensic science (along with a few cases of the dry heaves).

So I thought we would explore how our bodies serve as evidence – not as victims, but as perpetrators. Let’s examine the clues our bodies leave behind.

Say you commit a heinous crime, one that includes the deadly duo of rape and murder. There are myriad ways you can be linked to that crime. Let’s start with the tried-and-true method, fingerprints.

No two people share the same fingerprint. Even identical twins, who have the same DNA, will have differences in their fingerprints, since the “friction ridge skin,” as it is known in professional circles, is a result of many environmental factors, such as bone growth and conditions within the womb. And although Sir William James Herschel is credited with being the first to use fingerprints as a means of identification back in 1858, it seems the Chinese were about two thousand years ahead of the curve.

In “The Volume of Crime Scene Investigation - Burglary,” dated to around 200 B.C., the Chinese mention the use of handprints as evidence. They were also using fingerprints on clay seals to secure documents, which is pretty clever, considering they wouldn’t invent paper for another three hundred years.

It wasn’t until 1892 that fingerprints were first used to solve a homicide. That accomplishment goes to Argentina, whose Buenos Aires sleuths relied on prints to solve the Rojas murder case in which the mother of two brutally slain boys eventually confessed after her bloody fingerprint was identified at the crime scene.

But fingerprints are just the start of the biological trail. Let’s talk semen.

There are usually about two hundred million sperm swimming within a single ejaculate, making it the perfect fluid for DNA analysis. Even individuals who can’t produce sperm (aspermiacs) and those who have been clipped (vasectomized) can still be identified based on their seminal fluid. The test for semen at a crime scene is cheerfully known as “The Christmas Tree Stain,” since the reagents stain the sperm in blues, greens, and reds. Once the sperm are recovered, the DNA packed within each little swimmer can be matched to a culprit.

But semen is just one of several bodily fluids used in identification. Blood is another popular means of narrowing down, or eliminating, suspects. By identifying the grouping (A, B, O, or AB), the presence of Rhesus antigens (Rh factor), and certain genes, investigators are able to match or disqualify an individual based on their results.

Saliva is another common fluid recovered at crime scenes. It can be found on the victim, as can bite marks, or left on objects such as cigarette butts, glasse,s or cans of soda, and is another valuable source of DNA. But bodily fluids, which fall under the specialty of “forensic serology,” also include anything excreted or secreted from the body, including urine, vomit, oils from the skin, and feces.

And let’s not forget about hair. The human body sports around five million hair follicles. On average, we lose around one hundred hairs per day. The length and quality of the hair is based on the region of the body from which it sprouts and ancestry dictates whether it is light, dark, straight, or kinky. Microscopic characteristics of hair enable investigators to differentiate between individuals and to determine whether the hair has been chemically altered, thus providing another link between suspect and crime scene.

Whether it’s semen, blood, spit, or hair, our bodies, as living organisms, leave behind a biological trail. And as the science of forensics becomes more exact, that trail becomes easier to follow.

Something to think about the next time murder crosses your mind…

Here's the Smithsonian's excellent interactive website on forensic anthropology.

Enjoy and I'll see you next week!