A crucial tip from a passerby led authorities to identify the suspect involved in the tragic killings of two Brown University students and an MIT professor. This unexpected breakthrough arose from an unusual encounter on a sidewalk near Brown University, where a man known only as “John” in a police affidavit shared vital information with law enforcement.

John’s account is being credited by investigators as the pivotal clue that linked the suspect to the Brown University shootings and the subsequent murder of a Massachusetts Institute of Technology professor in Brookline, Massachusetts. The professor was found shot in his home just two days after the campus incident.

The Providence, Rhode Island community had been gripped by fear and frustration as the search for the shooter dragged on. More than 40 rounds had been fired inside a Brown University engineering building, leaving residents and students anxious and demanding answers.

However, six days into the investigation, a significant development occurred. Authorities announced late Thursday that the suspect had been found dead, an apparent suicide from a self-inflicted gunshot wound.

John’s timely intervention proved to be the turning point in this complex case, providing the key details that ultimately led police to the suspect.

“He blew this case right open,” said Rhode Island Attorney General Peter Neronha of the information provided by the individual that resulted in finding the gunman nearly 24 hours later.

“When you crack it, you crack it,” he said.

According to police, John had several encounters with 48-year-old Claudio Neves Valente before Saturday’s attack. As police posted images of a person of interest — now identified as Neves Valente — John began posting on the social media forum Reddit that he recognized the person and theorized that police should look into “possibly a rental” grey Nissan. Reddit users urged him to tell the FBI, and John said he did. The police affidavit said they learned about the tip on Dec. 16, three days after the shooting and a day after the tip line was created.

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.

The affidavit says John gave investigators additional critical details: he encountered Neves Valente in the bathroom of the engineering building just hours before the attack, where John noted the suspect’s clothing was “inappropriate and inadequate for the weather.”

John also bumped into Neves Valente outside, mere blocks from the building, where John watched Neves Valente “suddenly” turn around from the Nissan when he saw John. What ensued was then a “game of cat and mouse,” according to John’s testimony — where the two would encounter each other and Neves Valente would run away.

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

“The Suspect responded, ‘I don’t know you from nobody,’ then Suspect repeatedly asked, ’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.

“Respectfully, I have said all I have to say on the matter to the right people,” John wrote on Reddit Wednesday night.

As of Thursday, it’s unknown whether John will receive the $50,000 reward the FBI had offered for information about the Brown shooting.

Ted Docks, special agent in charge of the FBI, said it was possible when asked by reporters.

“It would be logical to think that, absolutely, that individual would be entitled to that,” he said.

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