A 70-year-old Santa Rita Jail inmate died early Sunday morning from injuries suffered in a beating, and the man's cellmate has been arrested in connection with the lethal assault inside a cell in the Dublin jail, an Alameda County Sheriff's sergeant said Sunday.

Alameda County Sheriff's deputies found Cesar Augusto Pajuelo on the floor of his cell at about 6 a.m. Sunday, "severely injured and unresponsive," Sheriff's Sgt. Ray Kelly said in a statement. Pajuelo was taken to Stanford Health Care Medical Center in Pleasanton, where he later died from his injuries.

Kelly said Pajuelo's cellmate, 19-year-old Paul Stefano, who was in the cell with Pajuelo when deputies found the injured inmate, was then arrested on suspicion of murder.

No motive for the sudden violent attack had been established by late Sunday afternoon, Kelly said.

Pajuelo has been at Santa Rita Jail since February 2018, having been booked for lewd and lascivious acts on a child under 14, and for continuous sexual abuse on a child under 14.

Stefano had been booked into custody at Santa Rita on March 6 for auto theft and possession of a stolen vehicle, Kelly said.

Alameda County Sheriff's detectives and crime lab personnel were still at the scene late Sunday conducting interviews and otherwise investigating.