Science - September 15, 2011

CSI Wageningen

His hair isn't windswept and he doesn't sport a leather jacket or sunshades. Rene Smulders, a researcher at Plant Research International doesn't look as if he's just walked off the set of CSI.

And yet he does help the Dutch Forensic Institute (NFI) solve murder cases by investigating the origins of plant spores. Smulders and his colleagues have published on one of the first pieces of plant evidence to be used in a Dutch court, in an article in Forensic Science International: Genetics.
Model species
Smulders' team was asked by the Netherlands Forensic Institute NFI to research the origin of plant matter on the car of a suspect. They went to the scene of the crime with the NFI and local detectives to take samples.
From the samples they had to select a representative or ‘model' species. A difficult choice to make, says Smulders. The model species needs to be one that is common and frequently leaves traces of its presence behind. They chose the common knotgrass, a plant with the added advantage of being an inbreeding species that rarely crossbreeds with other types of grass. This leads to local patches with little genetic variation, whereas over greater distances there are bigger differences. Smulders: ‘This gives a good balance between finding a perfect match and making sure it tells you something about the location.'
The researchers looked for knotgrass in the suspect's back garden and at several reference locations. Smulders compared the genetic ‘fingerprint' of the evidence material with the collected samples. The genetic barcodes of plants are comparable to human DNA profiles. In humans, these are created by examining the length of the replicated pieces of DNA. Smulders, on the other hand, cut up the DNA randomly using special enzymes. Bigger genetic differences then produce very different patterns. When the fragments are sorted into different lengths, you get a kind of barcode.
The idea, ultimately, was to see whether the genetic barcodes of the various plant samples could be linked together. Smulders: ‘It was exciting to see whether they were identical.' Initially the research did not throw up any perfect matches: a bit of a downer. But in the end statistical analysis linked the seeds very decisively to the vegetation at the scene of the crime. How did things go in the courtroom? Apparently the suspect was not found guilty, but this was nothing to do with Smulders' research. ‘The judge accepted the evidence.'