The inmate found dead Thursday at the Sonoma County Jail was a 57-year-old Santa Rosa man, according to the Marin County Sheriff’s Office, which is handling the investigation.

Michael Estes died in custody Thursday morning, said Marin County sheriff’s Lt. Doug Pittman.

Estes, whose name had been withheld until his family was notified, had a long history of undisclosed medical problems, Pittman said.

The inmate had not been involved in any confrontations and was alone in his cell when he called for help, Pittman said. Suicide and drugs are not suspected.

An autopsy will be performed by the Marin County Coroner’s Office. Acting Sonoma County Sheriff Rob Giordano chose to ask Marin County to investigate the death, an option allowed under an agreement between law enforcement agencies.