Pictured: Homeless hero 'John' who blew Brown University case open

A homeless Reddit user led police to the Brown University shooter after playing a chilling game of 'cat and mouse' with the killer.

The tipster, known only as 'John,' was previously identified by investigators as someone they wanted to speak to after he was believed to be 'in proximity of' the college shooter, police confirmed to the Daily Mail.

John encountered gunman Claudio Neves Valente in the bathroom of Brown's engineering building just hours before the deadly attack, according to the police affidavit. He also noticed Neves Valente's clothing was 'inappropriate and inadequate for the weather.'

John later bumped into Neves Valente outside, mere blocks from the building. He 'suddenly' turned around from the Nissan when he saw John, the tipster said.

The two then faced off in a 'game of cat and mouse,' according to John's testimony, where the two exchanged words before Neves Valente fled.

At one point, John says he yelled out 'Your car is back there, why are you circling the block?'

Neves Valente responded 'I don't know you from nobody' and then repeatedly asked John, "Why are you harassing me?"' according to the affidavit.

John told police he eventually saw Neves Valente approach the Nissan sedan once more and decided to walk away.

John previously attended Brown University, but is now homeless. He frequently sleeps in the basement of the Barus and Holley building, a law enforcement source told Fox News. 

As police shared images of the person of interest in the shooting - now identified as Neves Valente - John began posting on the social media forum Reddit that he recognized the suspect.

He theorized that police should look into 'possibly a rental' gray Nissan. Reddit users urged him to tell the FBI, and John said he did.  

'I'm being dead serious,' John's Reddit post said. 'The police need to look into a grey Nissan with Florida plates, possibly a rental.'

'I know because he used his key fob to open the car, approached it and then something prompted him to back away,' he wrote.

'When he backed away, he relocked the car. I found that odd so when he circled the block, I approached the car that is when I saw the Florida plates.'

Police learned about the tip on December 16, three days after the shooting and a day after the tip line was created, the affidavit said.

Up until that point, the police affidavit says officials had not connected a vehicle to the possible shooter.

That detail led them to get more video of a Nissan Sentra sedan with Florida plates and enabled Providence police officers to tap into a network of more than 70 street cameras operated around the city by surveillance company Flock Safety.

It also helped them identify Neves Valente as the person responsible for gunning down Massachusetts Institute of Technology (MIT) professor Nuno F.G. Loureiro.

'He blew this case right open,' said Rhode Island Attorney General Peter Neronha of John. 'When you crack it, you crack it.' 

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John, in a Reddit post Wednesday night, wrote: 'Respectfully, I have said all I have to say on the matter to the right people.'

Neves Valente, 48, a Portuguese national, was found dead in a storage unit in New Hampshire Thursday evening from a self-inflicted gunshot wound.

Investigators believe he is responsible for fatally shooting two students and wounding nine other people in a Brown University lecture hall last Saturday.

He then killed Loureiro, who was also Portuguese, two days later at his Brookline, Massachusetts home, nearly 50 miles from Providence. 

As far as investigators know, Neves Valente acted alone.

Brown University President Christina Paxson said Neves Valente was enrolled there as a graduate student studying physics from the fall of 2000 to the spring of 2001.

'He has no current affiliation with the university,' she said.

Neves Valente and Loureiro - who is also Portuguese - previously attended the same academic program at a university in Portugal between 1995 and 2000. 

Loureiro graduated from the physics program at Instituto Superior Técnico, Portugal's premier engineering school, in 2000, according to his MIT faculty page. 

The same year, Neves Valente was let go from a position at the Lisbon university, according to an archive of a termination notice from the school's then-president in February 2000.

Neves Valente studied at Brown on a student visa. He eventually obtained legal permanent residence status in September 2017. 

It was not immediately clear where he was between taking a leave of absence from the school in 2001 and getting the visa in 2017. His last known residence was in Miami.

After officials revealed the suspect's identity, President Donald Trump suspended the green card lottery program that allowed Neves Valente to stay in the United States.