Story highlights The University of South Alabama says the student was acting erratically

The school says the student charged the officer, who drew his gun

18-year-old Gilbert Thomas Collar was killed in the Saturday shooting

Authorities in Mobile, Alabama, are investigating why a University of South Alabama police officer shot and killed an 18-year-old freshman who they say was naked and acting erratically outside the campus police station early Saturday.

The campus officer heard a loud banging noise on a window at the station at 1:23 a.m. CT (2:23 a.m. ET) Saturday, the university said in a statement. 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."

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, the school said.

School spokesman Keith Ayers called it a "campus tragedy" for the university family but offered no other details, citing the active investigation.

The University of South Alabama, located in Mobile, enrolls about 15,000 students.

Wetumpka, located just north of Montgomery in the middle of the state, has nearly 8,000 residents.