CHOCTAW COUNTY, Okla. (KFOR) – Agents with the Oklahoma State Bureau of Investigation are looking into an in-custody death in Choctaw County.

On Aug. 18, officials say 64-year-old Charles Gilliland was assaulted by two inmates who were also being held at the Choctaw County Jail.

As a result of the assault, Gilliland was rushed to Choctaw Memorial Hospital before being flown to an Oklahoma City hospital.

Gilliland was treated and released from the hospital, which sent him back to the Choctaw County Jail.

Investigators say since Gilliland returned to the jail, he was being held in an isolated cell by himself.

On Aug. 31, Gilliland possibly suffered a medical event and stopped breathing.

Authorities say all efforts to revive him were unsuccessful.

Now, the OSBI is investigating Gilliland’s death.

If it is determined that the Aug. 18 assault led to Gilliland’s death, the inmates involved could face additional charges.

Gilliland was being held for first-degree murder in the death of Kevin Roberson in Boswell, Oklahoma in January.