Sheriff Ron Hickman told reporters at the scene of the shooting at Knight Transportation, that the co-worker who was killed appeared to be a supervisor. He did not release the names of those killed.

"The suspect is believed to have taken his own life after being terminated early this morning," the sheriff's office said on its Twitter feed. It added that the suspect, armed with a shotgun and a pistol, fired at multiple employees.

"Only the shotgun was used," Hickman said, adding that the shooting was "a retaliatory act."