DENVER — A school bus driver was killed and 15 students and three coaches were injured when the bus collided with a concrete pillar at the airport on Sunday evening.

The bus was picking up members of the Legacy High School football team, who were returning home from Denver International Airport after a football game in California, according to an update from the Adams 12 Five Star Schools website.

Sgt. Mike Farr of the Denver Police Department said at a press conference on Monday that that the bus driver made a left turn to return to the terminal loop instead of a right turn to leave the airport, and drove off the road and into the pillar. The bus was traveling at 30 miles per hour to 40 miles per hour at the time. Farr added that the speed limit on the road that the bus was traveling on is closer to about 15 miles per hour, and that it is unclear why the bus was there.

Passengers aboard the bus told investigators that the trip seemed to be a normal one until they started feeling the bumps from traveling off the road, and that there was no discussion with the bus driver about what was happening.  

Farr also said that investigators are looking into whether there was a mechanical problem with the bus, the driver suffered from a medical condition, or whether the collision was intentional, though he added that there is no evidence that would lead him to believe that at this time.

The impact of the crash and resulting damage to the front of the bus was so severe that the driver had to be cut out of the bus, according to NBC News.

Adams 12 Five Star Schools confirmed in an update on its website that the bus driver was named Kari Chopper. She had worked for the district for four years, and passed her last Department of Transportation physical on May 10.

“We extend our thoughts and prayers to everyone impacted by Sunday's accident and offer our heartfelt condolences to the family of our bus driver who tragically passed away,” the district stated on its website.

On Monday, all students who were hospitalized on Sunday had been released to their families, according to an update on the district’s website. The district crisis response team reached out to all students’ families who were on the affected bus, and provided support as needed. The team also provided support to about 20 additional students at the school.

The Denver Police Department posted photos of the crash on its Twitter page:

BREAKING: School bus crash @ DIA. Several transported in critical condition. Watch here for updates. pic.twitter.com/V9QtfqhP6D

— Denver Police Dept. (@DenverPolice) September 11, 2016