Science on trial… in a trial

Whilst doing my undergraduate degree, I developed a little bit of an addiction to CSI. I also have to admit that I am a bit of a CSI snob; only the original CSI, set in Las Vegas, will do for me! However, as well as forensic science being frequently depicted in a multitude of crime dramas, it seems that it is increasingly being relied on in the courtroom as evidence.  So here’s a rundown of where forensic techniques are currently at, and what the future of forensic science might be.


The old faithful in the crime detective’s manual. The friction ridges formed on the tips of your fingers while you are developing in your womb, your fingertips, are 100% unique to you. Minor scrapes, scratches and burns won’t even affect the structure of a fingerprint (only deeper wounds will wipe out a fingerprint). Highly skilled experts are required to analyse the many different facets of a fingerprint in order to connect it to a specific person. It’s not just a case of clicking a few buttons as the beautiful people in CSI do, but it is reliable.

In addition to the print, you also leave another gift to the detectives – bacteria.  We have a large diversity of them which live in and on our bodies (In fact, it is becoming increasingly obvious the remarkable effect that these bacteria on our health and development). Like fingerprints, the unique colonies of bacteria that live on your skin, are unique to you. Forensic scientists are therefore pretty keen to see if this can help them solve a ‘who-done-it’.

However, as the eloquent Ed Yong noted in a blog post last year, comparing ‘bacteria fingerprints’ might not meet the high standards required in forensic analysis. Ed describes the scepticism of David Foran, director of Michigan State University’s Forensic Biology Laboratory, in response to research published by Noah Fierer from the University of Colorado.

“But Foran is much more sceptical. He says that Fierer uses the word “match” throughout his paper but the word has a very specific meaning in forensics. “[A match] means that there are absolutely no incongruities between the data produced from a questioned sample and those from a known sample,” he explains. That’s very different to saying that a bacterial sample is more similar to those from person A than person B. “Perhaps it can be said it seems more likely person A touched an object than did person B, however we definitely cannot say person A did touch the object.””

But maybe there is a way to get more information from the humble fingerprint. A news story appearing in the New Scientist today (19th May, 2011) reports that researchers at the University of Sussex have made progress in developing a technique which measures the static charge in prints left of insulating surfaces. The reason for this technique – well, it could give insight into how old the print is!

Lie detector test

The seemingly old-fashioned polygraph still has a role to play in detecting liars. Despite its limitations, the polygraph is still much more reliable to the fMRI lit detector tests – something I have blogged about before.


Due to the popularity of countless detective shows, people are well aware of the power of DNA analysis. Any DNA containing biological tissue which remains at a scene can be used to identify someone. This is something that has been demonstrated recently when Osama Bin Laden was conclusively identified using DNA analysis.  A blog post written by Christie Wilcox at the time beautifully explains the process step by step.

Smells like… death?

Also, appearing on the newsfeed of the New Scientist this week is an article which tells the story of the trial of a young mother charged with murdering her 2 year old daughter. At present, it is receiving attention as the judge deliberates over whether to allow an air sample, collected from her car boot, might be used as evidence in the trial. The prosecution wants to present it as evidence that a dead body was held in the boot.

“If the evidence is accepted, it will be the first time an expert witness has been called upon to identify the smell of a decomposing body, although other odour samples have been used in trials in the past, says Christopher Slobogin from Vanderbilt University Law School in Nashville, Tennessee.”

Through detection of chemical compounds in the air sample which a dead body might have released, investigators believe that they have shown that a body was present in the car boot. However, this is controversial. Because chemicals given off by dead animals may be similar to those of a human body, it is possible that the ‘smell of death’ might actually be that of pizza leftovers.

However, like the fMRI lie detectors and biological fingerprints, although the ‘smell’ of air samples can show the presence of compounds, whether the technique gives a result with the certainty required from experts remains to be seen. As the New Scientist article succinctly sums up:

“”The Frye test says that the scientific evidence is admissible if the relevant community generally accept it,” says David Moran, clinical professor of law at the University of Michigan Law School in Ann Arbor.”

Science does have an authority in society. People trust science to ‘tell the truth’. A jury made up of lay people may not understand the nuances of statistical analysis and physiological variability, and so the probability that a result is a false positive must be kept to a minimum by ensuring rigorous high standards and  high levels of certainty.  To me, this is essential is maintaining public confidence in science.

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