Two people were killed and nine others injured after a gunman opened fire at Brown University in Providence, Rhode Island, on Saturday.

The following day officials said they had detained a "person of interest", but later said they were releasing that person, explaining that the evidence "now points in a different direction".

The attack on the campus brings the number of mass shootings in the US to 389 for this year, according to the independent analysis website Gun Violence Archive. It defines mass shootings as having four or more victims killed or injured, not including the attacker.

Here's what we know about Saturday's incident.

The gunman opened fire in a classroom at around 16:00 local time (21:00 GMT) on Saturday at the Barus and Holley engineering building at the eastern end of Brown's campus, according to officials.

Final exams were taking place in the building at the time of the shooting, the university said.

The engineering building is a seven-storey block that includes 117 laboratories, dozens of classrooms and three lecture halls.

An economics professor told local public media outlet Ocean State Radio that the shooting had taken place during a review session for her course, which was led by her teaching assistant.

"He said that the shooter came in the doors, yelled something - he couldn't remember what he yelled - and started shooting," Rachel Friedberg said.

"Students started to scramble to try to get away from the shooter, trying to get lower down in the stadium seating, and people got shot," she added.

On Saturday, investigators said they were not immediately sure how the suspect got inside the first-floor classroom.

Outer doors of the building were unlocked but rooms being used for final exams required badge access, Mayor of Providence Brett Smiley said.

Two students, who were studying in a nearby library when the active gunman alert came through, told the BBC they "stayed away from the windows" as they awaited a police escort.

Officers searched the floor, made them drop their bags and raise their hands before before being led out of the library, the pair said.

Brown University, one of the oldest higher education institutions in the US, is part of the Ivy League, a group of elite universities in the northeast of the country.

The university, which has more than 11,000 students, is in Providence, Rhode Island's capital city, which is located about 50 miles (80km) from Boston and 180 miles (290km) from New York City.

Two students were killed in the incident and nine others were injured.

Smiley told reporters on Sunday that one person was in a critical condition and seven others were in a stable condition in hospital. One person with less severe injuries was discharged, he added.

The identities of those killed or most of those injured have not yet been released, but Brown University President Christina Paxson told reporters in a press briefing that all the victims, including those killed and wounded, were students.

"This is a day that we hoped never would come to our community. It is deeply devastating for all of us," she said in a statement.

In a statement on Sunday, the university said that the families of the two students killed were being supported.

"There are not enough words of comfort for families who lose a child, but we will do all we can," Prof Paxson said.

On Sunday, the head of Durham Academy, a private school in North Carolina, said one of their alumna, Kendall Turner, was injured in the attack, US media reported.

"Our thoughts and prayers are with Kendall, her family, and all members of the Brown University community during this incredibly difficult time," said Michael Ulku-Steiner in an email to staff.

According to police, a ninth victim did not suffer a gunshot wound, but had non-life threatening injuries from fragments from a shooting "that had occurred near them".

The investigation is ongoing and authorities are searching for additional video evidence that could help them track down the suspect.

On Sunday, officials said they had taken a person of interest into custody, but later released them because they did not think that person was the same individual who was seen in CCTV footage.

That footage showed of a male suspect, walking away from the scene of the shooting wearing all black clothing.

There is no weapon visible in the video, and his face is covered. Officials also say a firearm was not found in a sweep of the building.

Some witnesses reportedly told officers he may have been wearing a camouflage grey mask.

One person was arrested before police determined they were not involved in the shooting and released them.

In a statement released by the university on Sunday, Prof Paxson said some areas of campus are still restricted as police continued their investigations.

She said around 2,000 students were relocated to safe locations the previous, adding that she was "deeply moved" by students and locals who opened up their homes.

Brown University said all remaining exams, papers and projects would not take place as scheduled.

US President Donald Trump, speaking to reporters as he returned to the White House from attending the annual Army and Navy football game, described the shooting as "a terrible thing".

"All we can do right now is pray for the victims and for those that were very badly hurt," he said.

Additional reporting by Pratiksha Ghildial