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A powerful method for deducing microbial relationships has been edging its way into civil and criminal investigations. But courts should proceed with caution.
Anaesthetist Juan Maeso led a seemingly respectable life in the coastal Spanish town of Valencia. But he had a secret. Over the course of at least a decade, at two different hospitals, he regularly skimmed morphine from his patients, injecting himself just before using the same needle to administer their doses.
In 2007, Maeso was found guilty of infecting at least 275 people with hepatitis C, four of whom had died from complications related to the disease. He was sentenced to 1,933 years in prison, although he is expected to serve only 20 under Spanish law.
To this day, Maeso protests his innocence, saying that a patient must have infected him with the hepatitis C virus (HCV). But the scientific evidence, which was published in full only last year, overwhelmingly suggests otherwise. In that work, Fernando González-Candelas and his colleagues at the University of Valencia analysed and categorized almost 4,200 viral sequences in an effort to disentangle the path the infection followed, using a process known as phylogenetic forensics.
The method, which marries classic evolutionary-biology practices with modern sequencing technology, is increasingly being used in criminal and civil investigations, and for biodefence. A paper published this month, for example, describes how the technique allowed scientists to trace the likely origin of an anthrax-laced batch of heroin that has been killing users across Europe since 2009.
But the intersection of this science with the legal system makes many uneasy, says Anne-Mieke Vandamme, an evolutionary geneticist at the University of Leuven in Belgium, who has worked on 19 criminal cases since 2002, mostly for the defence. Unlike DNA evidence, which is routinely used in legal settings around the world, the results of phylogenetic forensics are rarely definitive. “You can never prove guilt,” she says.
And there are social concerns. Many patient advocates feel that tracing the path of infection in civil and criminal cases may further stigmatize diseases such as AIDS. Now, as the field matures thanks to advanced sequencing and analytical tools, a team of experts led by Vandamme is trying to develop guidelines for best practice both on technical aspects of the work and on presenting the evidence in courts. She hopes, she says, “to make clear to lawyers, judges and prosecution officers the powers and limitations of these methods”.