After six days of searching and little in the way of major breakthroughs, the hunt for the man suspected of opening fire at Brown University on 13 December suddenly gathered steam.

Police believe Claudio Neves Valente, 48, killed two students inside a classroom in an engineering building before travelling to killing a professor from the Massachusetts Institute of Technology (MIT) at his home in Brookline, Massachusetts.

Despite investigators scouring CCTV footage for days and issuing multiple calls for information - including the promise of a $50,000 (£37,500) reward - it was only on Thursday when reports suggested a major breakthrough had been made.

Police say the key lead came from an anonymous Reddit user who initially posted online urging them to look up the suspect's car. After a search that spanned multiple states, they tracked the vehicle and found the suspect dead at a storage facility in New Hampshire.

'He blew this case right open'

Investigators have hailed a key figure - known only as "John" in a Providence police affidavit - as the source of vital information in tracking the suspect.

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

As images of a new person of interest were released on social media, "John" posted on Reddit and said he thought he recognised the man now known to be Neves Valente.

"I'm being dead serious. The police need to look into a grey Nissan with Florida plates, possibly a rental," the post read.

In the comments, other users urged him to contact the FBI.

Police had not connected a vehicle to the suspect until the man reported the Nissan to them, according to the affidavit. They were then able to find more video of the car by tapping into dozens of street cameras around Providence.

The city's Mayor Brett Smiley told CNN that the tipster was a graduate of Brown. He said he had been pictured in an image released by police, which prompted him to come forward.

"He provided the Reddit tip initially. Anonymously," he said.

"It's sort of an amazing sequence of events, but really turned out to be critical to our investigation. We're grateful to him."

Beyond the car, police say "John" provided other critical details to investigators and was "fully forthcoming".

They say he had several unusual encounters with the suspect before the shooting at Brown.

The affidavit says he encountered Neves Valente in the bathroom of the engineering building just hours before the attack at Brown. He became suspicious after noting the suspect's clothing was "inappropriate and inadequate for the weather".

"John" then followed the suspect out of the building where, according to police, he watched him "suddenly" turn around from the Nissan when he noticed he was being watched.

According to his testimony to police, a "game of cat and mouse" then played out in which the suspect would repeatedly run away after seeing "John".

And at one moment, the two men even spoke.

"Your car is back there, why are you circling the block?" "John" shouted at the suspect.

"I don't know you from nobody," he replied, according to the affidavit. "Why are you harassing me?'"

"John" told police he eventually saw Neves Valente approach the Nissan once more and decided to leave the scene.

"John" gave all of this information to police during his testimony.

"Respectfully, I have said all I have to say on the matter to the right people," he wrote on Reddit late on Wednesday.

The investigators were able to track the vehicle to an Alamo rental location in downtown Boston. And then, from the rental agreement, they found the suspect's name.

The car, meanwhile, was tracked close to the home of the MIT professor who was killed, 47-year-old Nuno F Gomes Loureiro. It was then found to have been driven to a storage unit in Salem, New Hampshire, where the suspect was found dead on Thursday.

Police are working to establish a motive for the two shootings, and have acknowledged there are still plenty of unknowns.

It is also not clear whether "John" will receive the $50,000 reward offered by officials for information, although FBI Agent Ted Docks was asked whether it was possible at a news conference on Thursday.

"It would be logical to think that, absolutely," he said. "That individual would be entitled to that." (BBC)

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