Minnesota prison officials say three correctional officers have resigned after the killing of one of their colleagues.

Officials say Officer Joseph Gomm was attacked Wednesday at the state’s flagship prison in Stillwater by an inmate serving time for homicide. Authorities haven’t released details about the assault.

A spokeswoman for the state Department of Corrections tells the Star Tribune that three officers later resigned, but that the reasons for their resignations won’t be made public. They worked at either the Stillwater prison or a facility in Oak Park Heights.

Gomm’s relatives said in a statement that they were devastated “by the senseless and tragic loss.” They also thanked Gromm’s colleagues and others offering support.

More than 1,600 inmates are housed at the century-old Stillwater prison. About a third of the prisoners are serving time for homicide.