But though the FBI is avidly looking for any detail that may shed light on the Chechen terrorist, they may already posses the answer to the riddle: Inside Tsarnaev's brain.
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Tsarnaev, an amateur boxer, may have been the victim of chronic traumatic encephalopathy (CTE), a degenerative brain disease caused in part by repeated head trauma.
Past boxing bout for Tamerlan (L) (Photo: AFP)
Those who suffer from CTE may exhibit impulsiveness, anger, paranoia, depression and violent bursts.
But the Co-Director of the Center for the Study of Traumatic Encephalopathy was wary of linking CTE and the bombing. "The Boston bombing was a planned attack,” said Dr. Robert Cantu in an interview for TIME magazine.
“There was no flipping out here, no impulsiveness. That’s not what you see with CTE in younger people.”
Tsarnaev brothers during marathon
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.
Though the bombing itself was apparently well-planned and executed, the brothers' behavior during the chase in Boston's suburbs was described as "amateurish and reckless."
According to the police, during the exchange of fire with Tamerlan he suddenly charged at the police forces – and seconds later was run over by his younger brother as he was fleeing.
Aquaintences of Tamerlan described a previous incident in which he was removed from a local mosque after a violent outburst.
Decisive prognosis of CTE can only be made by an autopsy, looking for tau proteins in the brain, which appear when neural connections are damaged.
But US authorities have not revealed whether they intend to dissect the bomber's body, and even if they do, if proper measures to preserve the brain tissue have not been made, it may be impossible to find evidence of CTE.
The connection between the disease and violent behavior is still uncertain. For instance, though an autopsy of Canadian wrestler Chris Benoit, who shot his wife and son and killed himself in 2007, revealed signs of CTE, researchers couldn't link them to his acts, again due to their premeditated nature.
Similar brain damage was also found recently with football player Junior Seau, who shot himself in 2012.
Before committing suicide, the athlete sent a message to his family asking his brain be given to medical research.
A few months later, it was discovered he suffered from CTE.
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