Jose Rivera, 22, was stabbed to death inside the Atwater Federal Prison in June 2008. Authorities say James Leon Guerrero held him down while Joseph Sablan stabbed him several times with an ice pick-style shank.
Guerrero has now agreed to plead guilty in exchange for a life sentence. He has a federal court hearing on Tuesday in Fresno.
Sablan is still set to go on trial and could face the death penalty if convicted.