And that’s the problem with looking for CTE in Tarnaev. Authorities haven’t revealed if they plan to examine his brain, and unless they have taken some necessary steps to preserve it for study they may have lost that option already. But it may not matter. “The Boston bombing was a planned attack,” says Dr. Robert Cantu, also of Boston University and co-director of the Encephalopathy Center. “There were lots of explosive devices put together in a very premeditated way. There was no flipping out here, no impulsiveness. That’s not what you see with CTE in younger people.” That doesn’t mean Tsarnaev didn’t have brain trauma related to his boxing. “I think he did,” Cantu says. It’s just that it may not have caused his criminal behavior.

That points to the difficulty of establishing any link between the condition of a brain and actions that may or may not result from it. Cantu points to the case of the late pro wrestler Chris Benoit, who killed his wife and son and then himself in 2007. When his brain was studied after he died, it showed signs of CTE—but here too it might have had little to do with his murderous behavior. “In Benoit’s case the behavior was again premeditated. It took place slowly, over the course of a weekend. He even sedated his son first so he wouldn’t suffer,” Cantu says. Criminally pathological? Certainly. But triggered by CTE? Probably not.