The suspect in last weekend's mass shooting at Brown University is dead from a self-inflicted gunshot wound, with investigators certain he also killed a Massachusetts Institute of Technology professor two days later, officials said on Thursday.

The gunman, identified as Portuguese national Claudio Neves Valente, 48, was found dead Thursday night in a storage rental facility in Salem, New Hampshire, where he had rented a unit last month, officials said.

Valente attended Brown University more than two decades ago as a PhD student in physics and was a former classmate in Portugal of slain MIT professor Nuno Loureiro, 47. Despite those links, authorities said that his motive in the killings remains a mystery.

"I don't think we have any idea why now, or why Brown, or why these students, why this classroom," said Rhode Island Attorney General Peter Neronha, at a Thursday night press conference in Providence, where the university is located.

Valente entered a building used for Brown's engineering and physics programs on December 13 and fired at least 44 rounds from his 9 mm pistol, killing two students and injuring another nine, according to the Providence police affidavit for his arrest.

Then, officials say, he fatally shot Loureiro inside his home before disappearing and leading investigators on a manhunt that stretched over five days. Authorities said two guns, including the 9mm pistol they believe was used in the killings, were found by his corpse.

In Boston, US Attorney Leah Foley said at a press conference that investigators had evidence that made them certain that Valente, who was living in Miami and was a lawful permanent resident of the United States, murdered Loureiro in his home in Brookline, Massachusetts.

Trump administration to halt diversity visa program

The Trump administration quickly pointed to Valente's permanent residency status as a reason to halt the Diversity Immigrant Visa program’s lottery system that awards green cards to people from countries with relatively low numbers of immigrants to the United States.

"This heinous individual should never have been allowed in our country," Homeland Security Secretary Kristi Noem posted on X late Thursday.

Noem said she would "immediately" implement a directive by President Donald Trump to pause the green-card lottery "to ensure no more Americans are harmed by this disastrous program."

Foley said Valente and Loureiro had attended the same academic program at a university in Portugal from 1995 to 2000.

Valente used a phone that was harder to track and did not use credit cards linked to his name, according to Foley.

"He was sophisticated in hiding his tracks," she said.

Valente also switched the license plates on his rental car in an effort to avoid capture, officials said.

Foley declined to provide many details about the evidence linking Valente to Loureiro's murder, but said video images showed a rental car Valente was driving near Loureiro's home. The IP address associated with Valente's phone was known to have accessed the internet in the vicinity of the slain professor's home on the day he was killed, Foley added.

Providence police chief Oscar Perez said at a press conference that investigators believe Valente acted alone.

Rental car breakthrough

The big break in the case came via information from a man who had seen Valente inside a bathroom in the Brown University building where he carried out the shooting a few hours later, Perez said.

The witness told police that he found Valente to be extremely suspicious and followed him out of the building and down a street.

The witness saw Valente unlock his rental car and later gave police a description of that vehicle and its license plate, Perez said. Police reviewed video, found the images of Valente's car, and from there could trace it back to the rental agency, according to officials and the police affidavit.

The rental agency's security video included Valente's face and showed him wearing the same clothing worn by the suspect in footage from the Brown University shooting, officials said. Investigators obtained his name from the car rental agreement, and they noted that license plate readers showed Valente had been in the vicinity of the university from December 1 until nearly two weeks later when he carried out the shooting.

Investigators in Providence had said that Valente, whose face was covered by a mask in video from the day of the Brown University shooting, escaped on foot into nearby streets after carrying out the campus killings. That prompted a search that relied heavily on residential security footage because of a lack of surveillance cameras in the classroom building and surrounding area.

Police released images and video of a man believed to be the shooter, based on survivor accounts, and repeatedly sought the public's help in identifying him. The footage showed the suspect walking in a nearby neighbourhood both before and immediately after the attack.