ST. LOUIS (AP) — Missouri Gov. Mike Parson has denied clemency for a convicted killer hours before the man is scheduled to be put to death.

Russell Bucklew has a rare medical condition that his attorneys say could result in a gruesome execution, which is scheduled for 6 p.m. Tuesday.

Defense attorney Cheryl Pilate confirmed Parson denied clemency.

Bucklew was convicted of killing Michael Sanders in 1996.

He suffers from cavernous hemangioma. He has blood-filled tumors in his head, neck and throat. A permanent tracheostomy in his throat helps him breathe. His attorneys said in the clemency request that if one of the throat tumors bursts, Bucklew could choke to death.

The U.S. Supreme Court gave the go-ahead for the execution in April; Pilate didn’t say if any last-minute court appeals are planned.