ST. LOUIS (AP) — A federal appeals court has refused to halt the execution of a Missouri inmate, hours before he is scheduled to be put to death.

A three-judge panel of the 8th U.S. Circuit Court of Appeals on Tuesday denied a stay of execution for Earl Ringo Jr., who faces lethal injection at 12:01 a.m. Wednesday for killing two people while robbing a Columbia restaurant in 1998.

It would be the eighth execution in Missouri this year and the 10th since November.

The appeal questioned Missouri’s use of the sedative midazolam prior to executions, claiming it could dull the inmate’s senses, leaving him potentially unable to express any pain.

Attorney Richard Sindel says he is appealing to the U.S. Supreme Court. A clemency petition is also before Gov. Jay Nixon.