(CNN) -- Authorities are investigating why a University of South Alabama officer fatally shot an 18-year-old freshman who they say was naked and acting erratically outside the campus police station early Saturday.
With few details of the shooting, the student's mother and one of his friends said they could not understand how a six-year varsity wrestler and good-natured teenager could have died under such strange and sad circumstances.
According to a statement from the school, the campus police officer heard a loud banging noise on a window at the station at 1:23 a.m. CT (2:23 a.m. ET) Saturday. When he left the station to investigate, the school said, "he was confronted by a muscular, nude man who was acting erratically."
The man, later identified as Gilbert Thomas Collar, of Wetumpka, Alabama, repeatedly rushed and verbally challenged the officer in a fighting stance, the school said.
The officer, whose name hasn't been released, drew his weapon and ordered Collar to stop, the school said. The officer retreated several times to try to calm the situation.
"When the individual continued to rush toward the officer in a threatening manner and ignored the officer's repeated commands to stop, the officer fired one shot with his police sidearm, which struck the chest of the assailant," the school statement said. "The individual fell to the ground, but he got up once more and continued to challenge the officer further before collapsing and expiring."
Collar's mother, Bonnie, said the two people who called her with the news of her son -- someone from the school and another involved in the investigation -- did not mention that her son was trying to attack anyone when he was shot.
"He was wearing no clothes and he was obviously not in his right mind," she told CNN. "No one said that he had attacked anybody, and obviously he was not armed. He was completely naked."
"The first thing on my mind is, freshman kids do stupid things, and campus police should be equipped to handle activity like that without having to use lethal force," Bonnie said.
Campus police immediately contacted the district attorney's office to request an external investigation, and the Mobile County Sheriff's Department will assist, the school said.
The officer has been placed on paid administrative leave pending the outcome of internal and external investigations, according to the school, which enrolls about 15,000 students.
Investigators are looking at security camera tape of the shooting, Collar's mother said.
Earlier Saturday, Ayers called it a "campus tragedy" for the university family but offered no other details, citing the active investigation.