ST. LOUIS (AP) – Attorneys for condemned Missouri inmate John Winfield are asking a federal appeals court to halt his execution.

Winfield is scheduled to die June 18 for killing two women in St. Louis County in 1996. His attorneys on Monday asked the 8th U.S. Circuit Court of Appeals to grant a stay, claiming that Missouri’s lethal injection process violates his constitutional right against cruel and unusual punishment.

It would be Missouri’s first execution since another convicted killer, Russell Bucklew, was spared on May 21, when the U.S. Supreme Court sent his case back to the appeals court.

Lethal injection has come under increased scrutiny since a botched execution in April in Oklahoma. Winfield’s attorneys also cite concerns about Missouri’s secretive method of obtaining execution drugs from an unknown compounding pharmacy.