By CBSLA Staff

SAN QUENTIN (CBSLA) ― A San Quentin inmate serving time for attacking his grandfather is now facing a murder charge for allegedly killing a fellow inmate who failed to register as a sex offender, authorities said.

Sammeon Waller (Photo via San Quentin State Prison)

Sammeon Waller, 28, is accused of killing 66-year-old John Sullivan, who was found unresponsive in his cell early Wednesday morning at San Quentin State Prison, according to correctional officials.

Sullivan was admitted from Placer County on March 3, 2016, to serve a 10-year sentence for failure to register as a sex offender, a second-strike.

He was pronounced dead shorty after 1 a.m., authorities said.

Investigators later identified Waller as the suspect.

John Sullivan (Photo via San Quentin State Prison)

Waller was admitted from Los Angeles County on Dec. 20, 2017, to serve seven years for first-degree burglary and injury after his conviction in the attack on his 82-year-old grandfather in Pomona.