Joseph Tui Jr., 32, was charged Monday with first-degree murder after he was accused of beating an Oahu Community Correction Center inmate to death on Saturday, according to prosecutors.
Bail has been set at $250,000. He is scheduled to appear in District Court Tuesday morning.
Tui is accused of assaulting his 76-year-old cellmate. Police say the beating lasted five minutes.
The beating happened while corrections officers were gathering the inmate counts, according to public safety officials.
Tui was serving time for a misdemeanor third-degree assault charge. If Tui is convicted of murder in the first degree, he will face life in prison without parole.