LINCOLN, Neb. (AP) — A Nebraska prisoner who died last month overdosed on a combination of methamphetamine and Ecstasy.

A death certificate issued to The Associated Press Thursday confirms that 22-year-old Daelan Lamere died because of the accidental overdose.

Prison officials previously acknowledged that Lamere had both drugs in his system when he was found unresponsive in his cell at the Tecumseh State Correctional Institution on May 27. He died at a Lincoln hospital on June 6 after his heart failed.

Lamere was sentenced to 6 to 11 years in prison for four counts of robbery and one count of use of a deadly weapon to commit a felony in Douglas County. He was scheduled for release in September 2020.