How Brain Scans Can Lighten Sentences In Murder Cases

An increasing trend of defendants using neuroscience to argue for lesser sentences

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A prison escapee convicted of killing a vacationing couple in their 60s—for their trailer, according to a newspaper from the couple's hometown—recently dodged the death penalty for his crime. Instead, John McCluskey, 45, will serve life in prison without parole. What may have swayed the jury against the death penalty were brain scans the defense presented, Wired reports. The scans showed that parts of their client's brain responsible for planning and controlling behavior were smaller than usual, among other abnormalities.

In recent years, judges and juries have seen more and more high-tech brain scans appear in court cases, NPR reports. Usually they're used to argue defendants can't bear full responsibility for their crimes because their brains are immature or impaired. For some scientists, this is troubling. "You can't leap from a dynamic brain scan to notions of responsibility," Nigel Eastman, who studies law and ethics in psychiatry at the University of London, told the U.K.'s The Guardian in November.

There's also evidence brain scans sway juries unduly, even compared to other scientific visual evidence such as charts and graphs. And they can appear in controversial cases: Attorneys have used them to argue against the death penalty in other violent murder cases. (Though it's not always clear, unless jurors say so, how much of an impact brain scans have on any one case.) About 5 percent of murder trials now draw on neuroscience, NPR reports.

Wired took a closer look at the neuroscience in McCluskey's trial using court documents and an interview with a neuroscientist who followed the proceedings. You can check out the argument for both sides over at Wired. McCluskey's defense argued that changes to his brain indicate he has a hard time planning and controlling his emotions and behavior. Meanwhile, the prosecution presented evidence McCluskey could still plan, from running a drug circle in prison to planning his own escape.