A Denver-area school where a shooting killed a teenager and wounded eight other students was without a resource officer because of a canceled sheriff's office contract.

Douglas County Sheriff Tony Spurlock said Friday his department did not renew its STEM School Highlands Ranch contract amid a dispute over resource officers' duties. Instead, the school hired a private firm.

A law enforcement official with knowledge of the case told The Associated Press on Thursday that a guard credited with capturing one of the suspects in Tuesday's attack fired his weapon inside the school. Two news organizations citing anonymous sources reported that authorities are investigating whether the guard mistakenly fired at a responding sheriff's deputy and may have wounded a student.

A Friday school statement said violence hits campuses with and without resource officers. It credited the guard, deputies and students with thwarting the attack.