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A Utah State Prison inmate has pleaded guilty to killing his cellmate in a fight last year.

Jacob Paul Ecker, 24, pleaded guilty Tuesday in 3rd District Court to a first-degree felony manslaughter charge for the April 27, 2011, beating death of Alfonso Lopez. Prosecutors originally charged Ecker with murder.

Ecker and Lopez, 27, were friends who had requested to bunk together at the prison. But, according to testimony at a preliminary hearing last year, tensions had been building between them.

Ecker later told detectives that he "let loose" on his friend and punched him twice.

"Once [Lopez] was on the ground, [Ecker's] rage continued," Unified Police Detective Christine Petty-Brown testified at that preliminary hearing. "He said he was sadistic and he enjoyed seeing Lopez hurt."

According to court documents, Lopez suffered a collapsed lung and a lacerated heart and liver as a result of the attack. He died of "massive internal bleeding."

"Usually when I see something like that it's a motor vehicle collision ... or blunt force trauma with a baseball bat," assistant medical examiner Pamela Ulmer testified last year. "I [saw] similar heart damage this week in someone who fell five stories."

Ecker was serving a term of up to five years on a number of felony counts stemming from a March 2010 arrest. Police found a hatchet in Ecker's backpack after he threatened a man's life at the Salt Lake City Main Library, according to court documents.

He faces up to life in prison when he is sentenced Jan. 15 by Judge Mark Kouris.