A convicted child rapist who was serving a 43-year sentence for multiple sex crimes was beaten to death by fellow inmates inside a Washington state prison, authorities said this week.

Robert Munger, 70, was attacked last Friday at the Airway Heights Corrections Center in Spokane County and died at a medical facility later that day. Officials confirmed his identity on Wednesday.

It was not immediately known how many inmates were involved or what exactly led to the killing.

The Department of Corrections is investigating and an autopsy is underway, spokeswoman Janelle Guthrie told news outlets.