The California students who barely managed to escape from a burning tour bus after a deadly collision with a tractor-trailer last year were never given the required safety instructions from the driver before the crash, according to documents released Wednesday.

The National Transportation Safety Board investigators questioned every student and were told that neither of the bus drivers on the trip told them about emergency exit windows or showed them a safety video as bus company Silverado Stages required by policy. More than half of the 29 students did not know which windows were deemed emergency exists, and some shattered other panels to escape.

Investigators still have yet to determine why the FedEx truck barreled across the median of Interstate 5 100 miles north of Sacramento and struck the bus carrying Southern California students on a visit to Humboldt State University in April 2014. The crash killed five students, three chaperones and the drivers of the bus and truck.

The NTSB has not reached any conclusions about the cause. It released 2,100 pages of documents in its ongoing investigation, including interview notes, photos and vehicle records.

A person who was driving behind the FedEx tractor-trailer told investigators that truck’s left turn signal turned on before it changed lanes and drifted across the median onto oncoming traffic. The truck driver, 32-year-old Tim Evans, made no attempt to slow down or change direction before the crash, according to eyewitnesses and physical evidence.

Evans’ wife told investigators that he was in bed for 10 hours before the crash and had no health problems. An autopsy showed no drugs or alcohol in his system at the time of the crash.

Maintenance and inspection records showed no defects in the truck.

Chaos followed the crash as students scrambled to escape out windows after the crash.

The woman at the wheel of the bus at the time of the crash had taken over for another driver in Sacramento.

The first driver told investigators he did not show a six-minute safety video, which includes a description of emergency exits, and did not remember if he told students how to escape the bus. The trip started with confusion over where to load the passengers.

"The whole thing just got so lost, you know," the bus driver said in an interview transcript. "So the audience, honestly, most of the time when I'm talking, they're just talking to each other and they don't listen."

One passenger said chaperones told students about emergency exits. Silverado Stages now requires drivers and clients to confirm they gave safety instructions, according to documents.

"If anything, this report does reveal a larger role that issues with the safety advisory by Silverado may have played in the injuries and deaths in this case," said Katherine Harvey-Lee, an attorney who filed lawsuits against Silverado Stages and FedEx on behalf of surviving passengers and the family of a victim.

Silverado Stages CEO John Busskohl declined to answer questions from The Associated Press because of ongoing litigation.

One student seated three rows behind the bus driver said he saw the FedEx driver with his head down and slumped toward the door immediately before the crash. Other students said they were asleep or didn't see the driver. Another witness who watched the crash from his lawn said he saw the FedEx driver's head moving as he crossed the median.

The names of witnesses were redacted in the documents.

The passengers of a sedan that was also struck by the FedEx truck said they saw flames coming out of one of the trailers. No other witnesses reported seeing the truck on fire, though, and a board expert found no evidence of flames before the collision.

Keith Holloway, a spokesman for the National Transportation Safety Board, said a final report may be issued this summer. California Highway Patrol spokeswoman Lacey Heitman said her agency is close to finishing its separate investigation into the cause of the crash, but could not give a timeline.

The Associated Press contributed to this report.