LINCOLN, Neb. (AP) — Prison officials say the Nebraska Department of Correctional Services is investigating a second incident of physical violence against staff this week.

The department says an officer was assaulted by an inmate Wednesday evening at the Nebraska State Penitentiary in Lincoln after he ordered the inmate to return to his cell. A second officer helped in subduing the inmate and was also struck.

The first officer struck was taken to a nearby hospital for non-life-threatening injuries and released.

Department Director Scott Frakes says he is “troubled” by the event but commends prison employees for a quick, team-oriented response.

Three prison staffers at the Tecumseh State Correctional Institution were assaulted by inmates Monday.