New York (AFP) – A manhunt for the mass shooter who opened fire in an exam room at one of America's top universities stretched into a fifth day Wednesday with no apparent police progress in identifying a suspect or a motive.

The only new information from police at a media briefing Wednesday was an appeal for a witness believed by investigators to have come close to the suspected gunman on the grounds of Brown University in Providence, Rhode Island.

The shooting happened Saturday, when a man with a rifle burst into a campus building at the Ivy League college where students were sitting exams. The man opened fire. killing two students then fleeing.

"Investigators are asking for the public's help in identifying and speaking to the individual shown in these photos who was in proximity of the person of interest," the Providence police department wrote on X with images of an individual wearing a grey hooded sweatshirt and a dark overcoat.

"They may have relevant information to the investigation," Providence police chief Oscar Perez told Wednesday's briefing.

Perez said this individual, who was not named, was "close enough" to the suspect "that we feel that we need to speak with them."

Perez also called on web users not to share artificial intelligence-generated images linked to the shooting.

The two students killed Saturday were Ella Cook, vice president of Brown's Republican Party association, and Mukhammad Aziz Umurzokov, originally from Uzbekistan, who had hoped to become a neurosurgeon.

One survivor was in critical but stable condition, five were in a stable condition, and two had been discharged from hospital, Providence's mayor Brett Smiley told the briefing.

Authorities initially detained a man in connection with the shooting, but they later released him.

The university has faced questions about its security arrangements after it emerged that none of its 1,200 security cameras were linked to the police's surveillance system.

"Why did Brown University have so few Security Cameras? There can be no excuse for that," US President Donald Trump wrote on social media.

The university issued a lengthy statement addressing the criticism, saying that its security cameras don't extend every part of the over 250 buildings on campus.

There have been more than 300 mass shootings in the United States so far this year, according to the Gun Violence Archive, which defines a mass shooting as four or more people shot.

Attempts to restrict access to firearms still face political deadlock.