BOSTON -- A man who died after he was shot inside a Harvard University dorm by a gunman who fled the scene has been identified.

Officers said Justin Cosby, 21, of Cambridge was shot in the abdomen before 5 p.m. Monday and taken to Beth Israel Deaconess Medical Center, where he died the following day.

"Subsequent investigation has revealed that the shooting took place inside of Kirkland House at Harvard," District Attorney Gerry Leone said.

Leone said that only Harvard University students are granted access to the area where the shooting took place and that it was subject to the same electronic security measures as the rest of the university. The university called the incident "isolated," and said the victim was not a Harvard student.

"We are still developing facts as to why (Cosby) was there," Leone said.

Leone indicated several people were involved in the incident.

"We do believe every body who was in the area was there because they may have known somebody in the Harvard community," Leone said.

Cosby, who grew up in Cambridge, lived at a home on Memorial Drive with his mother, Denise Cosby, and was attending Salem State.

She told NewsCenter 5 she doesn't know why her son was at Harvard and that "he was not a thug."

"He was enjoying life, and it is really, really unfortunate that someone decided to take his life from him for whatever reason, and I don't know that reason," she said. "He went to see a friend as far as I know. He didn't come back when he said, and that is when I got concerned."

Police roped off an area on Dunster Street and were continuing to look for clues early Tuesday, but students were being allowed back in the area.

"I heard three gunshots, but I don't know much about it because I was on the top floor and was not going to come out of my room when it happened," said student Kathleen Breeden.

Monday night, Harvard President Drew Faust visited students, who were advised to stay indoors in the dining hall or basement. Counseling was also offered and the university issued a statement saying it believed the shooting was an isolated incident.

Students who live in the dorm were told they might be able to negotiate schedules on final exams because of the disruption.