A death row inmate in Missouri who has long claimed his innocence and is scheduled to be executed in less than one week asked the US Supreme Court on Wednesday for a stay of execution, arguing his due process rights were denied during the yearslong legal battle to save his life.

Missouri death row inmate Marcellus Williams has been executed despite admissions from a prosecutor’s office claiming his innocence. Williams had been convicted of the 1998 murder of Lisha Gayle, a former reporter for the St. Louis Post-Dispatch.