FBI widens net in hunt for Brown University shooter

The suspected gunman who killed two students at a university in the US at the weekend remains at large as authorities appealed for help in identifying him.

Officials in Providence, Rhode Island, told a news conference that they still have not identified the attacker.

The two students killed at Brown University in the shooting on Saturday were 19-year-old Ella Cook and 18-year-old Mukhammad Aziz Umurzokov.

During the news conference, several video clips taken from cameras in the vicinity of Brown University were played, that show the possible gunman walking near the site of the shooting on Saturday, wearing dark clothes and a face mask.

Providence Police Chief Oscar Perez said investigators were hoping someone might recognise the person based on his body movements, posture and bearing.

He also said that police have evidence the person was in the area as early as 10.30am local time on Saturday, more than five hours before the attack, and that he was likely "casing" the scene.

Officials said they are confident the person in the video is the gunman, but they also have "zero" evidence as to the motive for the shooting, according to Rhode Island Attorney General Peter Neronha.

Authorities also released a timeline video comprised of surveillance clips from neighbourhood cameras and a car's dashcam tracking the person's movements both before and immediately after the shooting.

In one clip, the man can be seen at a distance walking from the building's car park toward the street, even as police cars with flashing emergency lights arrive at the scene. The final clip shows the man walking along that street just three minutes after the shooting.

Officials said there were limited cameras inside the engineering and physics building where the shooting took place, and that none had recorded any clear footage of the gunman.

Police have received more than 200 tips and are working through them, Chief Perez said. Mr Neronha defended the speed of the investigation, saying it was difficult but that it was "going really well" and asked the public for patience.

But the days-long search has prompted many residents in the College Hill neighbourhood near campus to stay behind locked doors, while many Brown undergraduate students left after the university cancelled classes and exams for the rest of the year.

Authorities initially detained another person of interest, a man in his 20s, early on Sunday, but they released him after concluding that he was not involved.

Public schools in Providence remained open, but the district cancelled after-school activities.

In addition to the two deaths, eight students were injured in the attack, and seven remain in the hospital, with one person in critical condition, officials said.

Brown said it had implemented enhanced security measures since the shooting, including doubling the university department of public safety's staffing and restricting entry to campus buildings.

The gunman had walked into an engineering building whose doors were unlocked while exams were taking place, according to police. He opened fire with a 9mm gun inside a classroom and then fled, triggering a campus lockdown that left students barricaded in rooms or hiding beneath furniture for hours.

Brown, which has nearly 11,000 undergraduate and graduate students, is one of the oldest and most prestigious universities in the United States.

Ms Cook was the vice president of the school's College Republicans and a "leading Republican voice at Brown," according to an X post from the New York Republicans Club.

In her hometown, she worked at an ice cream shop in high school, where her co-workers used to tell customers with pride that she was headed to a top-rated school.

Mr Umurzokov had moved with his family as a child to Virginia, where he graduated Midlothian High School this spring as a top-10 student. He had planned to become a neurosurgeon.

"He always lent a helping hand to anyone in need without hesitation, and was the most kind-hearted person our family knew," his family wrote in an online fundraising post. "Our family is incredibly devastated by this loss."

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.

During a Christmas event on Sunday at the White House, US President Donald Trump spoke briefly about the shooting, saying "things can happen" and wishing the injured to "get well fast."