A 39-year-old man who'd been in the Franklin County jail for about a week died at a Richland hospital Wednesday from "coronary failure," authorities said.
An autopsy is Saturday by the Franklin County coroner's Office to determine if it was natural causes.
The inmate's name was not released Thursday while coroner officials continue to track down relatives.
The man had been in custody for at least five days on a Pasco Municipal Court case, according to jail Capt. Rick Long.
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Medical staff had been checking on the man on a regular basis because he suffered from a medical condition, but it was during normal rounds at 2 p.m. Wednesday that corrections officers found him unresponsive in his single cell, Long said.
Officers did cardiopulmonary resuscitation until paramedics arrived. He was taken to Kadlec Regional Medical Center, where he later died, said Long.