ARDMORE, Okla. (AP) — A Texas softball team coach did everything he could to save four of his players who died when an 18-wheel tractor-trailer smashed into their bus in Oklahoma, a relative said Monday.

Investigators meanwhile tried to solve the mystery of why the truck suddenly veered into oncoming traffic on Friday night on Interstate 35, crashing into the bus carrying 15 softball players from North Central Texas College.

The coach, Van Hedrick, had been driving the bus and is suffering "deep emotional turmoil" from the crash, according to his mother-in-law, Charlene Ruzika. Hedrick visited two injured players in the hospital Monday, Ruzika said.

"He did all he could to help those girls survive," she said in a phone interview.

The truck driver, 53-year-old Russell Staley of Saginaw, Texas, declined to comment Monday when The Associated Press reached him by telephone. Oklahoma Highway Patrol Capt. Ronnie Hampton said Staley had told investigators that something in the cab of his truck distracted him, but emphasized that Staley's statement would not necessarily be taken at face value.

"The driver's statement is one piece in that puzzle of 100 pieces," Hampton said. "We will compare his statement with the other 99 pieces of evidence."

The four players killed were Meagan Richardson, 19; Brooke Deckard, 20; Katelynn Woodlee, 18, and Jaiden Pelton, 20. Two other members of the team remained hospitalized: Bailey Buchanan, 18, was listed in good condition; and 19-year-old Rachel Hitt remained in fair condition.

Hampton said Staley was driving alone on his way from North Texas to Oklahoma and he wasn't hauling any freight.

Staley drove an estimated 950 feet through the median and off the highway before wrecking the trailer in the middle of several trees, National Transportation Safety Board member Robert Sumwalt said Monday.

"It's pretty obvious that there was no swerving, no evasive steering maneuvers," Sumwalt told reporters. "The track through the grass, through the median, is very straight."

Harry Crabtree, vice president of safety for the trucking company involved, Quickway Carriers, declined to discuss Staley's employment or the circumstances of the crash, citing the ongoing state and federal investigations.

"Our hearts are broken over this," he said, adding that the company is cooperating with authorities.

Sumwalt said some passengers on the bus were not wearing seat belts, but that federal investigators had yet to determine if the girls who died were wearing them. Federal law does not require passengers on school or commercial buses to wear seat belts.

Grieving students at North Central's campus created a memorial of flowers, teddy bears and neon-yellow softballs inscribed with the names of the four who died.

"You can walk in there and it's just like a ghost town," said Lyndi Starr, a sophomore at the college. "Everybody's quiet. Nobody's saying much of anything. Most people are still in shock that it happened."

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Juozapavicius reported from Tulsa, Oklahoma.