MOBILE, Ala. >> 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.

An attorney for Collar’s family questioned why the officer wasn’t able to use nonfatal means to subdue him.

“Obviously something caused him to act in manner that was somewhat unusual. It still does not justify shooting him down unless there is something we totally missed,” said former Lt. Gov. Jere Beasley, who’s representing the family.

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

“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 after watching the video.

“It’s very powerful,” said Cochran, whose agency is investigating the shooting along with the local district attorney. The video will be shown to the family and reporters this week, but won’t be publicly released.

Beasley, the Collar family’s attorney, said another police employee was at the station with the officer. The officer called for backup but went outside before it arrived.

“They called for backup, but he goes out by himself without backup. Backup came almost immediately after the shooting. I understand one officer came,” he said. Still, Beasley questioned why the officer called for support when facing an unarmed student.

The sheriff talked with Beasley’s chief investigator on Monday, but he did not mention anything about LSD or alcohol.

“I was surprised it came out at the news conference without contacting the family through us,” he said.

He said there have been no discussions about a lawsuit.

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

Mobile County District Ashley Rich said a grand jury would 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 clinical director of a drug rehabilitation provider said authorities’ description of Collar’s actions didn’t match the typical behavior of someone who has taken LSD.

“It’s not typical that someone taking LSD would pound on windows or chase people,” said Jack Feinberg of the nonprofit Phoenix Houses of Florida, who isn’t involved in the case. “The aggressiveness part is something that is just completely foreign. But, of course, drugs are unpredictable, especially if someone has other mental problems.”

He said that the drug is more likely to have a mellowing effect, involving hallucinations. Authorities haven’t discussed Collar’s psychological condition.

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.

Collar graduated earlier this year from Wetumpka High School, where a vigil in his memory was planned for Tuesday night.

Friends and family have said 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 writers Phillip Rawls in Montgomery and Jay Reeves in Birmingham contributed to this report.