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 drew about 500 people Tuesday night. The crowd included students, wrestling teammates and people of all ages from the community.
Speaker after speaker at the vigil remembered Collar as a young man with a great sense of humor and a great love of life. His parents were sitting right behind the speakers. Many in the crowd alternated between laughter and tears.
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."
Associated Press writers Phillip Rawls in Montgomery and Jay Reeves in Birmingham contributed to this report.