Researchers in Boston are examining a brain sample from the gunman who killed 18 people in Lewiston, Maine. The team at Boston University's Chronic Traumatic Encephalopathy (CTE) Center will look to see if repeated exposure to explosives while serving in the military could have contributed to the unusual behavior that Robert Card exhibited before walking into a bowling alley and restaurant and opening fire.

Dave Philipps, who covers the military and veterans for The New York Times and wrote about the research, spoke with GBH’s Morning Edition co-host Jeremy Siegel about the process. This transcript has been lightly edited.

Jeremy Siegel: What do we know about Card's time in the military and his potential exposure to brain injury?

Dave Philipps: Well, what's interesting is that for several weeks, we knew almost nothing. The military's been very tight-lipped about it. What they told us at first was that Robert Card, who was a sergeant first class in Army Reserves, had been in the Army for almost 20 years. But he had a pretty humdrum resume. His career was a petroleum supply specialist, and he had never deployed. So there was no indication in there that he'd ever been in combat or had any sort of traumatic experiences.

What we found out by talking to soldiers who worked directly with Mr. Card is that he had a very different experience than the Army was telling us, probably. He had been a trainer every summer in a weapons course that all cadets at the Army's Academy at West Point have to take. And so for two weeks, he would work, for years, on a grenade range. And there he would stand right next to cadets. Each cadet had to throw two grenades, but there's 1,200 cadets. And so Mr. Card and his fellow soldiers who were working in those grenades that they were exposed to up to 2,400 grenades blasts a summer. And he did that for at least six years and maybe longer than that, which means that he was exposed in his Army career to, you know, easily more than 10,000 grenade blasts.

Siegel: What sort of effect could 10,000 grenade blasts have on someone's brain and their mental health state?

Philipps: The short answer is: nobody knows. But the military is starting to come to the realization that all sorts of weapons that it thought were safe to fire may actually be potentially dangerous if they're repeatedly fired and the brain is exposed to the shockwave that's given out. And this is mostly heavy weapons, things like artillery, shoulder-fired rocket launchers, heavy machine guns. But certainly grenades could be on that list.

What happens in that repeated exposure? Again, the science on this is very new. But autopsies of some veterans that have been exposed to careers of blasts like this show a common pattern of scarring between the gray matter, where executive function takes place in the brain, and the white matter that connects it to other regions of brain. And so essentially, communication and function in the brain may break down and cause all sorts of changes.

Siegel: So now researchers here in Boston are analyzing a sample of Card's brain. What could this analysis find?

Philipps: Well, this is a very big deal. This is the Boston University lab that looks at CTE. And I'm sure listeners will know that this lab's been working on understanding this problem in the brain for years and was really responsible for recognizing that CTE is repeatedly found in football players and other contact sports. Much less is known about how much CTE shows up in people who are exposed repeatedly to blasts from weapons. But what they'll do is they'll look at very, very thin slices of the brain under very, very nice microscopes and look for physical damage or some of the signs of old physical damage to the brain.

And, you know, will they be able to draw a causal connection between damage in the brain and an act of violence? No, I think that's impossible. But if they do find this damage, that will, you know, add to the picture of who Robert Card was and what he was going through. And I think it also will be really important to policymakers when they're thinking about, what do we need to do to try to protect people in uniform who may be exposed to these types of blasts regularly?

Siegel: Dave Philipps covers veterans and the military for The New York Times. Dave, thanks so much for joining us this morning.

Philipps: Thank you.

Siegel: You're listening to GBH News.