The driver of an 18-wheel tractor-trailer that collided with a bus and killed four members of a Texas community college softball team told investigators he had been distracted by something in his cabin before the accident, authorities said Sunday.

The truck was northbound on Interstate 35 near Davis, Oklahoma Friday night when it veered across the median and smashed into the bus carrying 15 members of the North Central Texas College women's softball team and driven by their coach.

The truck, driven by Russell Staley, 53, of Saginaw, Texas, continued off the interstate. Staley was treated for injuries and released. There were no charges pending against him.

"He (Staley) said he was distracted by something in the cabin," said Oklahoma Highway Patrol Capt. Ronnie Hampton, who declined to say what the distraction was. He said that investigators do not necessarily agree with Staley's explanation. The Highway Patrol will eventually turn over the results of its investigation to the local district attorney, who will decide whether to pursue criminal charges.

Hampton also said investigators had obtained search warrants to collect evidence from both the truck and the bus. Besides the deaths, a dozen people were injured in the crash, one of them critically. Oklahoma University Medical Center said the critically-injured player, Bailey Buchanan, 18, was upgraded to stable condition Sunday. Rachel Hitt, 19, remained in fair condition at Norman Regional Hospital, a spokeswoman said.

The team was returning from a scrimmage against Southern Nazarene University in Bethany, Oklahoma. The Texas college is located just south of the Oklahoma border in Gainesville.

Three of the players died at the scene and a fourth died at a hospital in nearby Sulphur, Oklahoma. The four players killed were identified by the Oklahoma Highway Patrol as Meagan Richardson, 19, Brooke Deckard, 20, Katelynn Woodlee, 18, and Jaiden Pelton 20. All were from towns in North Texas.

A prayer vigil was scheduled at the college's Gainesville campus Sunday night.

The National Transportation Safety Board, which is also investigating the crash, said Saturday that Staley was driving for Quickway Transportation of Nashville, Tennessee. The agency scheduled an update on its investigation later Sunday.

According to federal data, Quickway's safety record has been good in recent years.

Records with the Federal Motor Carrier Safety Administration show that Quickway had not been involved in a fatal accident in at least the past two years through Aug. 22. The company had not faced federal safety-related penalties in at least six years, based on available records. Quickway was registered with 327 trucks and 436 drivers.

The company's out-of-service rate for safety violations — those that would lead a driver to be pulled off the road — was 7.5 percent, below the national average of 20.7 percent, according to FMCSA.

Of 51 violations recorded in the past 24-month period, the highest number — 13 — were for failing to use a seatbelt. There were two instances of using a hand-held mobile device while driving. During that same period, there were no drug or alcohol violations.

Phone messages left Sunday at Quickway and an email sent to its vice president of safety and recruiting were not immediately answered.

Nationally, crashes involving a large truck or bus killed 4,281 people in 2013, little changed from the number of deaths in each of the previous three years.

I-35 is a major artery for truck traffic stretching from Duluth, Minnesota through the middle of the country to the Mexican border with Texas.