Survivors of a deadly bus crash are being interviewed, but it will take time for investigators to determine why an Abilene Christian University bus left the highway and overturned, a state trooper said Saturday.

"It will be months from now" if anyone is ever charged in the Friday night wreck that killed one person and critically injured four others, Trooper Phillip "Sparky" Dean wrote in an email.

The school-owned bus was carrying 12 agricultural studies students, three faculty members and a faculty member's wife from Abilene to Medina, where they were going to spend the weekend doing mission work at a children's home. Authorities say the 34-year-old driver, faculty member Michael Nicodemus, lost control as the bus was entering a bend on U.S. 83 near Ballinger. The vehicle hit a concrete culvert and did a complete roll, ejecting some passengers.

Anabel Reid, a student from Petersburg, was pronounced dead at the scene. The other 15 people on board were taken to area hospitals, where four were in critical condition, an ACU spokesman said.

Two hospitals have refused to provide condition updates. Officials at Community Hospital in San Angelo said Allison Dorshorst, 18, of Colleyville, was in stable condition there.

A spokeswoman at Hendrick Medical Center in Abilene said Naomi Cruz, 19, of Richmond, and Tiffany Lutz, 21, of Zelienople, Pa., were in critical condition, while Merissa Ford, 19, of Maple Valley, Wash., was in good condition.

Dean said investigators were talking to the survivors as they were able. Some were "very injured," he said.

Accident investigators also will return to the scene over the next few days or weeks before preparing a computer reconstruction of the crash.

"That gives the investigators additional information as we try to determine the cause of this one-vehicle, run-off-of-the-road rollover," Dean said. "It will take some time for all of this to happen."

He declined to comment on the cause of the accident, saying only that "a lot" of possibilities were being considered.

ACU junior Amanda Wilson, 20, of Walsenburg, Colo., told the San Angelo Standard-Times she suffered only some bruises in the wreck. She spoke at a candlelight vigil on campus late Friday in which students prayed and consoled one another.

"This is hard, and this has made it all easier," Wilson said. "I thank everyone here, I pretty much came straight over here."

Wilson and Reid were friends, and she described her as "an amazing person, always full of life and always a joy to be around."

Reid was among 23 ACU agricultural and environmental science majors who made the annual trip to the Medina Children's Home last year. She helped clear land, mow the yard and move in a new family, according to a 2010 story posted on the school website.