I’m often just as surprised by what forensic scientists can’t do as by what they can. In the Netflix documentary Making a Murderer, for instance, the question of whether police planted the main character’s blood at a crime scene comes down to whether or not the FBI can detect a common laboratory chemical called EDTA in a bloodstain.
On a TV crime show, this would be a snap. The test would take about five minutes and would involve inserting a swab into a magic detector box that beeps and spits out an analysis of every substance known to humankind.
In real life, there’s no common and accepted test in forensic labs for EDTA even today, nine years after the FBI tested blood for the Steven Avery trial featured in Making a Murderer. In that case, the FBI resurrected a test they had last used in the 1995 O.J. Simpson trial, and testified that the blood in question did not contain EDTA and therefore was not planted using EDTA-preserved blood from an evidence vial. (Avery was convicted.)
Questions about the test’s power and reliability have dogged the case ever since. There’s even an in-depth Reddit thread where fans of the Netflix show are trying to sort out the science.
Having worked in chemistry labs, it surprised me at first that this analysis would be difficult or controversial. After all, a quick search of the scientific literature turns up methods for detecting low levels of EDTA in everything from natural waters to beverages.
But the key here is that we’re talking about forensic science, not beverage chemistry. Beverage chemistry, in this case, is much more exacting. Was there really no EDTA in the blood swabbed from victim Teresa Halbach’s vehicle, or was the chemical simply too diluted or degraded to be detected with the FBI’s method? Could the test have missed a small amount of EDTA? It would be hard to say without further experiments that replicate crime scene conditions, experiments that essentially put the test to the test.
The reality is that forensic science today is a strange mix of the high-tech and the outdated, so questions about evidence like those in Avery’s case are not uncommon. Methods that we take for granted, like measuring a particular chemical, or lifting a fingerprint off a gun and matching it to a suspect, can be difficult—and far from foolproof. On the other hand, some of the real science happening now sounds like something dreamed up by Hollywood script writers, such as new methods aiming to reconstruct what a person’s face looks like using only their DNA.
Making a Murderer, whether it sways your opinion on Steven Avery or not, has done a service by getting people interested in something as arcane as EDTA tests, and by showing why real-life crimes are not solved nearly so neatly as fictional ones.
I see the messiness of forensic science all the time, because I scan its journals and often come across new studies that make me think either “you mean we couldn’t already do that?” or “I had no idea that was possible.” I’ve gathered a few recent examples for a quiz.
How well can you separate CSI fact from fiction? Here are a few crime-solving scenarios I’ve cooked up; see if you can tell which use real methods based on new forensic research. You’ll find the answers below.
- A skeleton is found buried in a shallow grave. The body’s soft tissues have completely decomposed, so only the teeth and bones remain. A forensic anthropologist examines the bones and reports that they come from a female who was five foot six inches tall, and obese. Could she really tell the person was overweight?
- The body of a white male in his 50s turns up on a nature trail, scavenged by animals. The victim’s bones show a number of puncture wounds consistent with animal bites, but x-rays reveal fine lines of different density in the bone around some of the punctures. An expert says these lines show that the wounds were made about 10 years before death. Is it possible to tell the approximate age of these wounds from x-rays?
- A woman is found dead in her home, bludgeoned to death. A bloody frying pan lies on the floor next to her. Her husband is the main suspect. Fingerprints on the pan’s handle are too smudged to make a definitive ID, but an analyst says she can still rule out the husband: All of the fingerprints on the pan came from a woman, the expert says. Is it possible to tell if the fingerprints were from a male or female?
- A woman is sexually assaulted and identifies her male attacker in a lineup. The suspect’s DNA matches DNA found on her body. It looks like an easy case for the prosecutor—until the suspect reveals that he has an identical twin. Neither twin admits to the crime. Is it possible to tell which twin’s DNA was found at the crime scene?
- A witness sees a man in a stocking mask rob and shoot a man outside his home. A stocking is found near the house, and a hair-analysis expert testifies that 13 hairs in the mask are all human head hairs from an African-American. A microscopic analysis matches the characteristics of one hair to a particular African-American suspect. The prosecutor tells the jury that the chances are one in ten million that this could be someone else’s hair. Can hairs be matched to an individual this accurately?
- Yes. Biologists have long known that greater body mass changes the weight-bearing bones of the legs and spine, and a new study shows that even bones that aren’t supporting most of the body’s weight, such as arm bones, have greater bone mass and are stronger in obese people. So even in a skeleton missing its legs, our forensic anthropologist might be able to tell that the person was obese.
- No. This one is from an actual episode of Bones (The Secret in the Siege, Season 8, Episode 24, reviewed here by real-life bioarchaeologist Kristina Killgrove). In the episode, Dr. Temperance Brennan uses Harris lines to determine the age of bone injuries in two victims. Harris lines are real, but they form only in growing bones, so are useful only in determining childhood injuries or illness.
- Yes. A study published in November showed that the level of amino acids in sweat is about twice as high in women’s fingerprints as in men’s. Of course, as with all the new methods, this one could face challenges as evidence in a U.S. court of law, where the Daubert standard allows judges to decide whether scientific evidence is admissible based on factors including its degree of acceptance by the scientific community.
- Yes, if you do it right. Standard DNA tests don’t distinguish between twins, who are born with nearly identical DNA, but it’s possible to do a more sophisticated test to catch post-birth mutations and epigenetic differences, which you can think of as genetic “add-ons” that don’t affect the DNA sequence itself. One new test distinguishes between twins by looking for small differences in the melting temperature of their DNA that are caused by such epigenetic modifications.
- No. The field of hair analysis has come under heavy scrutiny, especially after a review by the U.S. Justice Department revealed major flaws in 257 out of 268 hair analyses from the FBI. The case described here is the real-life case of Santae Tribble, convicted in 1978 of murder. In 2012, DNA tests showed that none of the hairs matched Tribble—and one was from a dog.