The suspect in the mass shooting at Brown University last weekend is dead, officials said on Thursday, as investigators said he also killed a Massachusetts Institute of Technology professor two days after the rampage at Brown.

Officials said the gunman, identified as Portuguese national Claudio Neves Valente, attended Brown University more than two decades ago, but his motive remains a mystery.

US Attorney Leah Foley in Boston said Valente, 48, was deceased. He had been a PhD student in physics who was familiar with the building where the shooting took place, officials said.

Providence police Chief Oscar Perez and Rhode Island Attorney General Peter Neronha, speaking at a Thursday night press conference, said that Valente took his own life and investigators believe he acted alone.

Perez said a tip from a person who confronted Valente inside a bathroom on Brown’s campus led police to a car he had rented from an agency in Massachusetts.

There, police were able to obtain store footage of Valente in which he was seen wearing the same clothing seen in footage from the Brown University shooting, and found his name on the rental agreement.

Ted Docks, the FBI’s special agent in charge of the Boston office, told reporters that the suspect’s body was found in a storage unit in Salem, New Hampshire, where a large contingent of law enforcement officers descended Thursday night. Salem is about 30 kilometres north of downtown Boston.

Valente had rented the storage unit where his body was found, Neronha said. He added that investigators don’t know why Valente carried out the shooting, or why he chose to do so in the building he targeted.

“I don’t think we have any idea why now, or why Brown, or why these students, why this classroom,” Neronha said. “That is really unknown to us.”

Foley, the top prosecutor in Boston, said at a press conference that investigators were certain Valente “murdered MIT professor Nuno Loureiro” on Monday, saying that prosecutors have ample evidence linking him to the crime.

One official in Providence said that it’s believed Valente and Loureiro attended the same university in the Portuguese capital, Lisbon.

Foley said that once investigators have some understanding of Valente’s motive, it would be shared with the public.

MIT professor fatally shot

Two students at the Ivy League school were killed, and at least eight were wounded on Saturday.

Although officials said earlier this week they did not see a connection between the Brown University rampage and the death of a Massachusetts Institute of Technology professor who was found fatally shot on Monday, they now believe the two events may be linked.

Loureiro was killed in his home in the Boston suburb of Brookline, Massachusetts, some 80km north of Brown’s campus. He was a member of the departments of nuclear science and engineering and physics, as well as MIT’s Plasma Science and Fusion Centre.

Investigators in Providence said the suspect in the Brown University shooting escaped on foot into nearby streets, prompting a search that relied heavily on residential security footage because of a lack of surveillance cameras in the classroom building and the surrounding area.

Police released images and video of a masked man believed to be the shooter, based on survivor accounts, and have repeatedly asked for the public’s help in identifying him.

The footage showed the suspect walking in a nearby neighbourhood both before and immediately after the attack, including moments when police vehicles arrived with flashing lights.

Police also circulated photos of another unidentified man seen near the area, saying they wanted to speak with him as a potential witness who may have relevant information.

Authorities initially announced a person was in custody a day after the shooting, but later released that individual after determining he was not involved.