Maine mass shooter had a brain injury. Experts say that doesn't explain his violence.

Brain injury experts are cautioning against drawing conclusions from newly released and limited information about the Army reservist who killed 18 people last year in Maine’s deadliest mass shooting. Boston University researchers who analyzed a sample of Robert Card’s brain tissue say they found evidence of traumatic brain injury, including degeneration in the nerve fibers allowing communication between different brain areas. Card is believed to have been exposed to repeated low-level blasts as an Army hand grenade instructor. It is unknown if that caused his brain injury and what role brain injury played in his declining mental health. An Army spokesperson calls the lab findings “concerning” and described new efforts to protect other soldiers from blast injuries.