LINCOLN, Neb. (AP) — The family of an inmate killed in a 2015 riot at a prison in southeast Nebraska has sued the state.

The mother of Shon Collins says in the lawsuit filed Tuesday in Lancaster County that the state failed to protect him and that the Tecumseh prison was not properly staffed on May 10, 2015, when the riot broke out. Authorities have said the 46-year-old Collins and fellow inmate Donald Peacock were killed by other prisoners, but none has been charged.

The lawsuit does not list a specific figure being sought, but the family had sought $1.2 million in damages when it filed a claim against the state in 2016.

A spokeswoman for the Nebraska Correctional Services Department said Wednesday the department doesn’t comment on pending litigation.