Casey Anthony on trial (Image: Joe Burbank/AP/PA)

Update: On Tuesday 5 July Casey Anthony was found not guilty of killing her daughter, Caylee Marie.

Original article, dated 17 May 2011:

In a case that is gripping the American public, young mother Casey Anthony has been accused of murdering her 2-year-old daughter. As jury selection for the case continues, speculation is growing as to whether the judge will allow a sample of air, collected from the trunk of her car, to be presented as evidence of the “smell of death”.


The prosecution want to submit a report, prepared by Arpad Vass, from Oakridge National Laboratory in Tennessee, which concludes that the air sample contains the key chemical compounds of human decomposition, as well as a large concentration of chloroform. Some media reports are even suggesting that the jury might be asked to smell a can of the air in court.

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.

Whether or not an air sample can reveal the presence of a corpse in a car trunk relies on a number of factors, says James Covington from the University of Warwick, UK, in particular how long the corpse was in there and whether the chemicals given off had time to seep into the upholstery. If enough of these chemicals are absorbed, they could continue to be released for some time after the corpse is removed. These chemicals might be detected through analysis of an air sample taken directly from the trunk, or obtained by heating a sample of the trunk’s interior. In this case, both types of sample were submitted to Vass for analysis.

Frye test

It is the first time the smell of a human body will have been presented as evidence in court, so it needs to pass the Frye standard – a test to check that new scientific evidence stands up to scrutiny. “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.

Vass has long been on the hunt for a molecular signature given off by a decomposing body that could be used to identify the time of death or to track down clandestine graves.

While most research into decay is done on pigs, Vass has been working with real cadavers at Tennessee’s Body Farm, a research centre where researchers study the effects of decomposition on real bodies.

He has been working with the FBI to create a database of the chemical compounds that make up the smell of decomposing human remains. In one study Vass buried four human bodies and analysed the gases given off over a period of four years. He identified eight major classes of chemicals. This means he now has a database of chemicals found in the smell of a dead body against which to compare the air from Casey Anthony’s trunk.

Pizza leftovers

Vass identified five of these chemical classes in the trunk of Anthony’s car. He also compared the chemicals in the sample with those given off by decomposing animals to check that the smell came from human remains. He also conducted a number of control tests to compare against the sample, including the smell given off by a decomposing pizza. Anthony’s mother claimed the smell in the car trunk could have been caused by pizza leftovers.

The question now is whether the judge will accept that this evidence passes the Frye test. As this is a specialist field, it could be hard for the prosecution to convince the judge that Vass’s work is backed by a community of peers.

However, the judge could reject the evidence on different grounds, says Moran. In cases where the prosecution’s case seems especially strong – as in high-profile cases like this one – the judge might elect not to introduce questionable evidence because that could make it easier for the verdict to be reversed in a court of appeal.

As to whether the jury will be asked to smell the sample, “that would be shocking”, says Moran.