GEOFF BENNETT: Investigators are still trying to determine the motive behind two shootings in New England after the suspect was found dead last night.

The man who killed two students and injured nine others at Brown University was located in New Hampshire last night following a manhunt that ended at a storage facility.

Authorities say they were able to link the suspect to the murder of an MIT professor who was killed in his home on Monday.

Stephanie Sy has the story of how one anonymous tipster changed the course of the investigation.

PETER NERONHA, Rhode Island Attorney General: He blew this case right open.

He blew it open.

STEPHANIE SY: A crucial tip from a Reddit user is what led authorities to identify the gunman, bringing almost a weeklong manhunt to an end.

LEAH FOLEY, U.S.

Attorney: Law enforcement collectively believe that we have the person -- that we identified the person, and that person is dead, and that he was the person responsible not only for the Brown shootings, but for the Brookline shooting.

STEPHANIE SY: The Reddit tipster, known as John, told police he had suspicions about a man he'd seen hours before the shooting in the bathroom of the engineering building.

We now know that man was Claudio Valente.

John said he followed Valente after he left the building to a Nissan with a Florida plate.

The police affidavit describes an interaction between them, with John describing Valente as saying: "I don't know you from nobody.

Why are you harassing me?"

Hours later, the suspect killed two students and wounded nine others in the engineering building.

John's observations enabled police to tap into a network of over 70 street cameras around the city.

PETER NERONHA: When you do crack it, you crack it.

And that person led us to the car, which led us to the name, which led us to the photographs of that individual renting the car, which matched the clothing of our shooter here in Providence, that matched the satchel.

STEPHANIE SY: Police tracked Valente to a storage unit in Salem, New Hampshire, where he was found dead from a self-inflicted gunshot wound.

He'd been dead for two days.

Because the same Nissan was spotted near another crime scene, Valente is now believed to have also killed MIT Professor Nuno Loureiro, who was murdered in his home in Brookline, Massachusetts, on Monday, two days after the mass shooting at Brown.

Loureiro is believed to have crossed paths with the suspect when he lived in Portugal.

His former employer, the Institute for Plasmas and Nuclear Fusion, described Loureiro as a brilliant scientist whose presence -- quote -- "profoundly marked all those who worked and interacted with him."

Between 1995 and 2000, Loureiro attended the same academic program as Valente, a Portuguese national.

Valente then moved to the U.S.

on a student visa in 2000, enrolling as a physics graduate student at Brown.

He took a leave of absence from the program in 2001 and never graduated, becoming a legal permanent resident of the U.S.

in 2017 and living in Miami.

Hours after details of the suspect came out, President Trump said he would pause the diversity visa program Valente used to gain permanent residence.

Meanwhile, after a week of heightened fears in the Brown community: BRETT SMILEY (D), Mayor of Providence, Rhode Island: Our Providence neighbors can finally breathe a little easier.

CHRISTINA PAXSON, President, Brown University: Nothing can really fully bring closure to the lives that have been shattered over the past week, but this may allow our community to move forward.

STEPHANIE SY: The tipster is being hailed as a hero and is, according to FOX News, homeless.

For the PBS "News Hour," I'm Stephanie Sy.

GEOFF BENNETT: And we're joined now by Juliette Kayyem, a former assistant secretary at the Department of Homeland Security.

She's now at the Harvard Kennedy School of Government.

Thanks for being with us.

We appreciate it.

JULIETTE KAYYEM, Former U.S.

Department of Homeland Security Assistant Secretary: Thank you for having me.

GEOFF BENNETT: So what more should we know about this tip from someone using the social media platform, Reddit, that ultimately led authorities to the suspect?

JULIETTE KAYYEM: Yes, so Reddit is a platform where lots of casual information is shared, where people learn how to fix a car, to really bad information.

It's not generally -- this is very unique.

Let's just put it that way.

What we know now is that there is a person, his name basically -- we didn't know who he was.

His name is now described as John, who encounters the killer at a couple of moments, a couple hours before the mass shooting, encounters him near the car.

This John decides to go on Reddit and urge the police to follow the license plates, says, this guy was suspicious, we had an interaction, but doesn't immediately tell the police.

We later learned that John had been at Brown a long time ago.

He's been homeless for some period of time and may not have felt confident going to the police.

The police then see this, and there's some sort of interaction between this John and the police.

That is what the police say sort of blew the case open in a good way, because now they had a car and a license plate, and then, by then, then they could figure out who had rented the car, who he might be.

They had a name, they had a picture and things unfolded very quickly after that.

GEOFF BENNETT: This case is as unusual as it is unsettling and tragic.

What stands out to you about it?

JULIETTE KAYYEM: I mean, there's two pieces.

I mean, one is just the nature of the killings.

One is a mass shooting in a classroom, sort of anonymous.

It's sort of against an institution.

And the other one against the MIT professor looks more like a targeted assassination.

In this world of sort of this kind of violence, you don't get the same person generally doing those two types of things.

So this was odd.

And I will admit that I was skeptical about the connection between the two killings until you started to see more evidence.

I think the second piece is, of course, just the grudge factor.

We don't have a specific motive, but I think rational people can look at the evidence we now have and see that this was -- Brown was a university that he did not succeed at.

And the MIT professor was a person who he overlapped with in Portugal.

And then he became an MIT professor and heralded as a leader in nuclear theory, while the suspect or the killer sort of did not amount to much.

That length of the grudge, the sort of that long-term stewing, where no one is -- no one around him is sort of capturing that, that is very, very odd, as you said, sort of disconcerting.

And I don't know how one stops that.

Like, I mean, just it was a multidecade grudge.

GEOFF BENNETT: We know that President Trump has suspended the green card lottery program that allowed the suspect to come into the country.

What do you make of that move?

JULIETTE KAYYEM: So, Valente came in two different periods in his life.

One was as a student visa when he attended Brown.

He then leaves.

There's then these, like, gap years.

But then, in 2017 -- so, remember, this is during the Trump first administration -- he comes on what's called a diversity visa.

It's just a way of describing visas that are given to people who lawfully can enter this country, stay in this country, have no criminal record, but they're from countries that we don't get a lot of representation from, Portugal being one of them.

He has no -- Valente had no criminal record, no suspicion of incitement, nothing.

I mean, he's just sort of -- as I said, he's just sort of stewing there.

One could, as the Trump administration often does, sort of make a sweeping generalization about this status visa or other status visa.

But I have to admit, the Trump administration has been against the diversity visa for a long time.

This may just be a sort of way for them to have a compelling reason to close the program down.

It's a relatively small program.

But, of course, closing down this immigration program doesn't really solve -- doesn't really solve violence in this country.

I mean, in other words, just because you're reacting to one incident with one immigrant, we have lots of violence in this country committed by all sorts of people.

And I'm not sure that a sweeping condemnation of everyone who comes on the diversity visa program is a solution to the violence problem.

It is, for the Trump administration, a solution to their long-term animosity towards this visa program and most lawful immigration programs.

GEOFF BENNETT: Juliette Kayyem, thank you for joining us.

We appreciate it.

JULIETTE KAYYEM: Thank you.