Another San Diego County inmate has died in custody, the 13th this year.

Twenty-eight-year-old 28-year-old Franklin July died on Sept. 16 at an unspecified county jail. July had been arrested on suspicion of transporting, selling or furnishing drugs.

The Sheriff's Department told California's Department of Justice the death was natural.

However, the San Diego Union-Tribune says the Sheriff's Department didn't announce the death publicly and declined to discuss the case.

The paper says it only learned of the death Monday after filing a state Public Records Act request.

The Union-Tribune has been investigating deaths in county jails. There have been at least 141 deaths since 2009.

The paper says the county has the highest jail mortality rate among California's six largest counties over the past decade.