by Bing Guan

A manhunt was underway Monday after a mass shooting at elite Brown University left two dead and nine wounded and US authorities said they were releasing a man initially detained as a person of interest.

The shooting took place Saturday in a building where exams were underway on the Ivy League campus in Providence, Rhode Island. A man with a rifle burst in and opened fire before fleeing.

News that a person was being held indicated a breakthrough, with FBI Director Kash Patel announcing that local police had given federal investigations a lead.

But authorities had to walk this back, saying late Sunday that there was not enough evidence to connect the person to the shooting.

"I think it's fair to say there's no basis to consider him," Rhode Island Attorney General Peter Neronha said.

A lockdown and shelter-in-place order went into effect immediately after the shooting, as heavily armed officers flooded the area. But the latest news meant renewed fears for the college town and state capital.

"We know that this is likely to cause fresh anxiety for our community," Providence Mayor Brett Smiley was quoted as saying by US media.

All the victims were students. Of the nine wounded, one was in critical condition, seven were in stable condition and one has been discharged, Smiley said.

Joseph Oduro, a teaching assistant at Brown, said he was in a campus auditorium when the gunman entered.

"I was standing in the front of the auditorium, and he came through the back, so we pretty much directly made eye contact, and then as soon as that happened, I looked at my students and signaled them to come to the front, and then I just ducked," Oduro told CNN.

"He came in, pointed the gun and then screamed something... then he just started shooting right after that."

Police released 10 seconds of footage of the suspect, seen from behind, walking briskly down a deserted street after apparently opening fire inside a first-floor classroom.

"It is shocking and so terribly sad. I know the students here, many of whom were sheltering for many, many hours last night," Smiley said later on CNN. "They're all incredibly shaken up."

Final exams scheduled for Sunday were postponed, university officials said.

Latest mass shooting

The attack is the latest incident of mass shooting in a country where attempts to restrict access to firearms face political deadlock.

"This should not be normal," Smiley said on CNN. 

"This should not be the case that every community needs to prepare for something like this to happen. And I certainly never thought that it would actually happen in Providence, although we were well prepared for it."

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

Emergency alert

Brown, which has around 11,000 students, issued an emergency alert at 4:22 pm (2122 GMT) on Saturday reporting "an active shooter near Barus and Holley Engineering," which is home to the engineering and physics departments. Two exams had been scheduled at the time.

"Lock doors, silence phones and stay hidden until further notice," the university said.

Law enforcement and first responders swarmed the scene, with local news station WPRI reporting "clothing and blood on the sidewalk."

The deadliest school shooting in US history took place at Virginia Tech on April 16, 2007, when South Korean student Seung-Hui Cho killed 32 people and wounded 17 others before taking his own life.