Shredded connections deep in the brain. Battered and scarred blood vessels that are no longer able to support neurons. Clumps of dead cell debris marking a long pattern of injury.

The results of the autopsy of Robert R. Card II, the Army Reservist who killed 18 people, then himself, in the deadliest shooting in Maine’s history, left little question that his brain was profoundly damaged. But the finding raises other questions that have broad implications for the military and for the nation’s millions of veterans.

Mr. Card was a grenade range instructor who never deployed to combat. He is not known to have ever hit his head in a serious car crash, he never played football, and he does not appear to have had any other accidents that might account for the damage to his brain.

His only exposure came from routine training blasts on the training range — at a level that is supposed to be safe.

If those blasts were still strong enough to profoundly damage his brain, as it appears happened, then how many other troops are being exposed to the same risk? How many veterans may be struggling with similar injuries that have gone unseen or been misunderstood? How should those veterans be treated if they seek mental health care, or are accused of crimes?

“The implications are just so large,” said Frank Larkin, a former Navy SEAL and sergeant-at-arms of the U.S. Senate, whose son, Ryan, also a Navy SEAL, died by suicide and was found to have extensive brain damage from blasts.