Campus officials said the confrontation was recorded by security cameras. The video and other information has been turned over to the district attorney and the Mobile County Sheriff's Office, which will review the shooting.
Colgan Meanor went to high school with Collar and then enrolled at the same college.
"He was a great, loving guy who always made people smile," she said. "He's not the kind of guy that people knew him and said he would do something like this."
Collar was the second person killed on the South Alabama campus since last year.
A university freshman was charged with murder in the fatal stabbing of another teenager who was slain in an on-campus apartment in July 2011. The victim was a visitor to campus and was not enrolled, authorities said.
Ayers said South Alabama, located near downtown Mobile, was still "a very safe campus," despite Collar's death.