A specialized laboratory examining the brain of the gunman who committed Maine’s deadliest mass shooting found profound brain damage of the kind that has been seen in veterans exposed to repeated blasts from weapons use.

The lab’s findings were included in an autopsy report that was compiled by the Maine chief medical examiner’s office and released by the gunman’s family.

The gunman, Robert Card, was a grenade instructor in the Army Reserve. In 2023, after eight years of being exposed to thousands of skull-shaking blasts on the training range, he began hearing voices and was stalked by paranoid delusions, his family said. He grew increasingly erratic and violent in the months before the October rampage in Lewiston, in which he killed 18 people and then himself.

His brain was sent to a Veterans Affairs laboratory in Boston that is known for its pioneering work documenting chronic traumatic encephalopathy, or C.T.E., in athletes.

According to the lab’s report, prepared on Feb. 26 and updated on Wednesday, the white matter that forms the wiring deep in the brain had “moderately severe” damage, and in some areas was missing entirely. The delicate tissue sheaths that insulate each biological circuit lay in “disorganized clumps,” and throughout Mr. Card’s brain there was scarring and inflammation suggesting repeated trauma.