GEOFF BENNETT: There are new details tonight about the man believed responsible for exploding a Tesla Cybertruck last week in front of the Trump Hotel in Las Vegas.

Police and military officials now believe Matt Livelsberger suffered post-traumatic stress disorder, and we now have some of the final words that he wrote that might help explain the end of the life of a decorated Special Forces soldier.

Here's Nick Schifrin.

NICK SCHIFRIN: Matthew Livelsberger was a warrior, a career Special Forces soldier known as a Green Beret.

In 13 years, he deployed nine times, including five times to Afghanistan, and rose to become an intelligence, then team sergeant with the rank of master sergeant.

But his final days were spent on leave, stopping at Tesla charging stations on a circuitous route from Colorado to Las Vegas, where he died by suicide, before exploding his rented Tesla Cybertruck in front of Trump Tower.

In notes on his phone released by Las Vegas police, he called out -- quote -- "Military and vets, be prepared to fight to get the Dems out of the fed government."

But he also wrote: "Why did I personally do it now?

I needed to cleanse my mind of the brothers I have lost and relieve myself of the burden of the lives I took."

U.S. officials confirmed Livelsberger, like so many other warriors, suffered trauma from service, including a reported traumatic brain injury.

He also suffered moral injury.

QUESTION: You want to read the e-mail?

SAM SHOEMATE, Former U.S. Army Intelligence Officer: Yes.

NICK SCHIFRIN: That, he detailed to Army intelligence officer SAM Shoemate, who read a Livelsberger e-mail on "The Shawn Ryan Podcast."

In the e-mail, Livelsberger admitted he participated in a 2019 strike in Afghanistan that he said killed hundreds of civilians and a subsequent cover-up.

Livelsberger was also in touch with an ex after splitting up from his second wife.

SPENCER EVANS, FBI Special Agent in Charge: It ultimately appears to be a tragic case of suicide involving a heavily decorated combat veteran who is struggling with PTSD and other issues.

NICK SCHIFRIN: Army officials confirmed he was in therapy -- quote -- "Livelsberger had access to and used the Preservation of the Force and Family program.

He did not display any concerning behaviors at the time and was granted personal leave."

That was just days before his life ended in Las Vegas.

For additional perspective, we turn to retired army brigadier general Stephen Xenakis, a psychiatrist with extensive experience working with veterans with PTSD and traumatic brain injuries.

Stephen Xenakis, thanks very much.

Welcome back to the "News Hour."

When you look at Master Sergeant Livelsberger's deployments, when you read what he wrote in that suicide note released by the police and that e-mail to Sam Shoemate, what do you see?

BRIG.

GEN. STEPHEN XENAKIS (RET.

), U.S. Army: Well, it's tragic.

And, unfortunately, it's a story that we have heard at other times.

It's a story that comes out of all these 20 years of warfare and goes back, actually, many, many years, thousands of years.

These men and soldiers, these men and women that go through these multiple deployments under these circumstances are really events, and the stress and the trauma pile up on them.

And you have all these factors in play with him.

You have his sense of moral injury, which is a guilt and shame that comes with what soldiers do and haven't done, knowing that there's a core ethical principle that they live by.

It's very individual, but that is a common principle that we have that is very important in terms of justifying or being able to make sense out of the activities, actions that have to be undertaken in war.

You have the stress, and it comes out as post-traumatic stress.

There is traumatic brain injury, which he -- there's evidence that he also suffered that, that there's injury and damage to the brain.

Very often, these soldiers also have other injuries and musculoskeletal pain.

They have problems with sleep.

We don't know in this particular circumstance if there was self-medication, sometimes prescribed medications.

All of this piles up.

And, over time, it just gets to be too much.

NICK SCHIFRIN: And... BRIG.

GEN. STEPHEN XENAKIS: And -- I'm sorry.

NICK SCHIFRIN: No, no, it's OK.

Sorry to interrupt you, but can PTSD, can the reported traumatic brain injury that his ex-girlfriend reportedly say, can that really drive someone like him to do what he did?

BRIG.

GEN. STEPHEN XENAKIS: Well, what happens is, it piles up, and there's a period where the soldier copes as best as - - the soldiers copes as best as they can.

And they're able to go through their daily life, have relationships, and then at some point it gets to be too much.

Maybe it's part as they get older, as they get more responsibilities, as they're thinking back and haunted by the memories.

And it's almost like they fall off a cliff.

And it can be very precipitous.

And they get into a very dark place in their life.

So it's the piling on, it's the cumulative effect of all these different circumstances that they're living with.

(CROSSTALK) NICK SCHIFRIN: And how does that -- sorry.

Forgive me again.

And how does that interact with his apparent family issues?

He reportedly split from his second wife just days or weeks before January 1, with whom they had a very young child.

BRIG.

GEN. STEPHEN XENAKIS: Well, there's a lot of stress, right?

And they're having problems in day-to-day coping, and that can particularly play out in intimate relationships and family relationships.

And then that feedback loop of, well, I can't do this, I can't do that, I don't have people that are supporting me, I don't have people that are caring, understand what's going on, and things just -- their lives just get worse.

And they're more -- their struggle gets even harder.

So there's no one factor here.

It's the connection of all these factors.

It's the whole is much more than the sum of the parts.

And what's important in terms of being able to care for these men and women, for our soldiers, for our veterans, is really experiencing them and engaging them as the whole person that they are, and realizing that each of these problems that they're facing will over time cause them to feel worse and maybe get to a desperate situation, as this man got to.

NICK SCHIFRIN: You talk about experiencing with them, engaging with them.

In the minute or so that we have left, is the U.S. military doing enough, in your opinion, to provide mental health services to service members?

BRIG.

GEN. STEPHEN XENAKIS: Well, look, they're trying as hard as they can.

Look, these are tough problems.

And even in very -- with experienced clinicians, there are people that, for whatever reason, don't seem to be able to get better.

Is there more to do?

Well, that's an obligation we have as military physicians, as leaders, to keep thinking about, what more can we do?

What are we going to learn from this incident?

What are we going to learn from all the others?

And what can we do to improve our support?

Warfare is tough.

And people bear the burden and struggle with it.

So the military is doing what it can.

We do that as part of that.

But we have got to continue to put more energy and time to improve our support for our service members and their families.

NICK SCHIFRIN: Psychiatrist and retired Army Brigadier General Steve Xenakis, thank you very much.

BRIG.

GEN. STEPHEN XENAKIS: I'm glad to help.

Thanks.