Police detained one person of interest on Sunday after a gunman dressed in black killed at least two people and wounded nine others at Brown University on Saturday during final exams at the Ivy League campus in Rhode Island.
University President Christina Paxson said 10 of those shot were students. Another person was injured by fragments from the shooting, though it was unclear if that victim was a student.
The attack occurred in the Barus & Holley building, a seven-storey complex that houses the School of Engineering and physics department in Providence. The suspect opened fire in a first-floor classroom where final exams were taking place.
Police described the suspect as a man in dark clothing last seen leaving the engineering building. Security footage showed him walking away, but his face was not visible.
Some witnesses reported the man, possibly in his 30s, may have been wearing a camouflage mask, according to Timothy O'Hara, deputy chief of Providence police.
Investigators believe the shooter used a handgun, according to an official who spoke on condition of anonymity.
Authorities were examining how the gunman gained access to the classroom. Outer doors of the building were unlocked, but rooms being used for final exams required badge access, Providence Mayor Brett P. Smiley said.
Officers searched the campus and surrounding neighbourhood late into Saturday night, combing through academic buildings, backyards and porches. A shelter-in-place order remained in effect on Sunday.
"The unthinkable has happened," Rhode Island Governor Dan McKee said, pledging all resources would be deployed to catch the suspect.
Nine people with gunshot wounds were taken to Rhode Island Hospital, where one was in critical condition. Six required intensive care but were stable, and two were in stable condition, hospital spokesperson Kelly Brennan said.
Some students sheltered for hours after hearing what they described as "loud pops." Police in tactical gear evacuated students from nearby buildings approximately five hours after the shooting, escorting them to a fitness centre.
US President Donald Trump said he had been briefed on the incident, telling reporters "all we can do right now is pray for the victims."
Rhode Island has some of the strictest gun laws in the US. Last spring, the state's legislature passed an assault weapon ban prohibiting the sale and manufacturing of certain high-powered firearms, set to take effect in July.
