CONCORD, N.H. (AP) – Authorities were investigating a fight between two murderers at the New Hampshire State prison that left one with stab wounds during the weekend.

William Sullivan, 20, was treated at Concord Hospital and sent back to the prison after a fight shortly after 9 a.m., Saturday, Corrections spokesman Jeff Lyons said.

Stephen Mann, 33, is accused of stabbing Sullivan with a homemade weapon.

Mann and Sullivan are serving life without parole.

Mann was convicted in November for shooting and bludgeoning his wife, Kelly Mann, inside their home. Their young daughters were home at the time of the 2004 murder.

Sullivan was convicted in July for murdering his girlfriends mother, Jeanne Dominico in 2003. Sullivan and the girlfriend, Nicole Kasinskas, plotted the murder because Dominico had prevented them for marrying.

Corrections officers witnessed the prison attack and broke it up in a matter of seconds, Lyons said.