PROVIDENCE, R.I. (AP) — Information from a tipster who had a strange encounter with another man on a sidewalk outside Brown University was key to police identifying the suspect they believe killed two students at the school and then two days later gunned down a Massachusetts Institute of Technology professor.

Known only as John in a Providence police affidavit, the source is being hailed by investigators as the key figure who gave law enforcement the details needed to determine who was behind the Brown shooting, as well as the killing of a Massachusetts Institute of Technology professor.

Ever since a shooter unloaded more than 40 rounds inside a Brown engineering building, anxiety and frustration has plagued the Providence, Rhode Island, community as police appeared no closer to identifying the person.

Yet, on the sixth day of the investigation, the case gathered steam, culminating in police announcing they had found the suspected gunman dead from a self-inflicted gunshot wound.

The tipster, John, was the reason why.

“He blew this case wide open,” said Rhode Island Attorney General Peter Neronha about the information provided by John that led to identifying the gunman.

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. He recognized the person and theorized to the police about possibly a rental grey Nissan. Reddit users urged him to inform the FBI, and John claimed to have done so.

Up until John's tips, police had not connected a vehicle to the shooter. John’s details allowed law enforcement to gather video evidence and utilize a network of over 70 street cameras in the city.

The following day, police released a new video showing Neves Valente fleeing from another man. Despite his earlier silence when contacted by the Associated Press, John returned to Reddit to update users that he had been interviewed by police.

Furthermore, John’s account provided essential details regarding encounters with Neves Valente, including a meeting in the bathroom of the engineering building just hours prior to the attack.

In a strange twist of events, the investigation led to a tense back-and-forth between John and Neves Valente, characterized as a “game of cat and mouse.”

As the investigation concludes, the community remains shaken by the events that transpired at Brown University.

Authorities have yet to confirm whether John will receive the $50,000 reward offered for information leading to the arrest in these violent shootings. The FBI hinted that it could be possible.