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.

This was not C.T.E., the report said. It was a characteristic pattern of damage that has been found before in military veterans who were repeatedly exposed to weapons blasts during their service.

“While it is unclear whether these pathological findings are responsible for Mr. Card’s behavioral changes in the last 10 months of life, based on our previous studies it is likely that brain injury played a role in his symptoms,” the report concluded.

The findings have grave implications for the military, because Mr. Card never saw combat, and had never been exposed to explosions from enemy fire or roadside bombs. The only blasts that hit his brain came from training that the Army said was safe.

“We know very little about the risks of blast exposure,” said Dr. Ann McKee, who leads the lab and signed the report. “I think these results should be a warning. We need to do more investigation.”

Congress has been pushing the military in recent years to investigate whether the blasts from repeatedly firing heavy weapons cause brain damage, but the military has proceeded at a halting pace that has yielded few changes in the field.

Soldiers like Mr. Card are still being exposed to large numbers of blasts from grenades, mortars, cannons and rocket launchers in training every day. And current Pentagon guidelines say that absorbing thousands of grenade blasts, as Mr. Card did over his career, poses no risk to troops’ brains.

In a statement on Wednesday, the Army said it had issued recommendations in recent months to reduce blast exposure in combat units. “The Army is committed to understanding, mitigating, accurately diagnosing and promptly treating blast overpressure and its effects in all forms,” the statement said. “While prolonged blast exposures can be potentially hazardous, even if encountered on the training range and not the battlefield, there is still a lot to learn.”

For much of his life, Robert Card was a quiet, friendly, dependable man with no history of causing trouble, his family said. He grew up on his family’s dairy farm in Bowdoin, Maine, and drove a delivery truck for work. He liked to fish in local ponds with his son, and often took his nieces and nephews along.