Investigators say the drivers of a school bus and semi that crashed in southern Nebraska both contributed to the fatal collision. The State Patrol released a statement Thursday on behalf of local investigators, who concluded that the vehicles entered the intersection in rural Webster County at about the same time.The September crash near Blue Hill killed the truck's driver, 21-year-old Travis Witte, of Blue Hill; and 59-year-old bus driver Marla Wentworth, of Red Cloud. Also killed were 18-year-old Dustin Tesdahl and 10-year-old Caroline Thallman, both students from Blue Hill. Five students were injured. Investigators say both drivers had an unobstructed view. Witte didn't have a commercial license required to drive the truck, and Wentworth failed to yield. Authorities say drugs and alcohol were not involved.