BOSTON (AP) -- A Massachusetts prisoner rights organization is criticizing the state prisons department for failing to complete an investigation into the death of a mental health patient in a department facility nearly five years ago.

Joshua Messier died after a scuffle with guards at Bridgewater State Hospital in May 2009.

Messier’s death was ruled a homicide, but none of the seven guards in Messier’s cell the night he died have been punished or prosecuted.

Leslie Walker, executive director of Prisoners’ Legal Services, told The Boston Globe "the tortoise-like pace" of the investigation is "unthinkable."

While refusing to address criticism directly, the district attorney’s office has previously said the criminal probe was dropped because the medical examiner could not identify a specific cause of death.

Messier’s parents have filed a lawsuit in the case.