MOBILE, Ala. (AP) — A nude University of South Alabama freshman had taken LSD and assaulted others before he chased the campus police officer who fatally shot him, authorities said Tuesday, though the student wasn't armed and didn't touch the officer.

Mobile County Sheriff Sam Cochran said at a news conference that 18-year-old Gil Collar took the potent hallucinogen during a music festival Saturday before assaulting two people in vehicles and attempting to bite a woman's arm.

Authorities said Collar then went to the campus police headquarters, where he was shot by university police officer Trevis Austin. Austin is on leave while investigators review the shooting.

Video taken by a surveillance camera showed Collar nude and covered in sweat as he pursued the retreating officer more than 50 feet outside the building, Cochran said. Collar got within 5 feet of Austin and the officer fired once, striking the student in the chest, Cochran said.

Cochran said Austin came out of police headquarters with his gun drawn after he heard Collar — a 5-foot-7, 135-pound former high school wrestler — banging on a door. While campus police typically carry pepper spray and a baton, Cochran said Austin was armed only with a gun during the confrontation.

The sheriff said it was unclear whether the officer could have avoided the shooting even if he had a non-lethal weapon to subdue the student.

"Had the officer had a Taser or some other less lethal instrument I don't know if that officer would have had an opportunity to shoulder his pistol and to use something else because the events were evolving so rapidly and he was approaching so close," Cochran said.

Cochran said he had "serious concerns" about the killing of an unarmed student when he first heard what had happened, but he better understood the officer's decision to open fire after watching the videotape of the shooting.

"It's very powerful," said Cochran, whose agency is investigating the shooting along with the local district attorney. The video was being shown to reporters and Collar's family but wasn't being publicly released.

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Investigators are trying to determine who provided Collar with LSD and could charge that person in Collar's death, Cochran said. Cochran said the information about Collar taking the drug came from people who were with him at the concert.

Mobile County District Ashley Rich said a grand jury would review the case and decide whether to charge the officer in the shooting, although it wasn't clear when. She said allegations of drug use also could wind up before a grand jury if investigators identify the supplier.

The effects of LSD can include extreme changes in mood and hallucinations and can last for hours.

Meanwhile, critics of the officer's actions are using Facebook to put together a protest of the shooting outside the campus police department on Wednesday morning. Organizers didn't immediately respond to messages seeking comment.

In a statement issued Tuesday, University of South Alabama President Gordon Moulton said the school is cooperating with authorities and expressed condolences to Collar's family.

"The university is committed to a full and thorough investigation of this matter," he said.

Collar graduated earlier this year from Wetumpka High School, where a vigil planned in remembrance of the longtime prep wrestler will be held Tuesday night.

Friends and family have said that Collar was courteous, kind and popular in high school. They said the actions before the shooting were out of character for him.

Collar wasn't known as a troublemaker and had only two minor scrapes with the law, according to court records: a speeding ticket and a citation for being a minor in possession of three cigarettes in March. He paid a $25 fine for the tobacco possession.

Two acquaintances at the university have said that before the shooting Collar was out of sorts and appeared intoxicated. He was screaming profanities in the street and running around naked, said South Alabama student Bronte Harber.

Student Sarah Hay said Monday that Collar was the loudest of a group of four or five young men and some of the others were trying to get him to calm down. She said he was talking about being on a "spiritual quest."

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Associated Press writer Jay Reeves in Birmingham contributed to this report.