Updated

Lawyers for a condemned Alabama inmate made a series of legal filings trying to halt his upcoming execution, arguing there are questions about the sedative that will be used.

Robert Melson is scheduled to die by lethal injection Thursday for the 1994 fatal shooting of three employees during a robbery at a Popeye's restaurant in Gadsden, 60 miles (96 kilometers) northeast of Birmingham.

Attorneys for Melson asked the 11th U.S. Circuit Court of Appeals and the Alabama Supreme Court Wednesday to block the execution. The 11th Circuit had previously issued a stay that was overturned by the U.S. Supreme Court.

Melson's attorneys argue the sedative midazolam is ineffective and noted a December execution in which an inmate coughed and heaved for 13 minutes.

The Alabama attorney general's office has argued midazolam's use has been upheld.