Updated

A man convicted of killing a mentally disabled East Texas woman by strangling her and beating her with a hammer nearly two decades ago wants the U.S. Supreme Court to stay his execution.

If it goes ahead as scheduled Thursday evening, Robert Ladd's execution will be the second in Texas this year.

Ladd's attorneys are arguing in the Supreme Court that the 57-year-old man is ineligible for the death penalty because he's mentally disabled. He's also part of a separate lawsuit that questions the potency of the sedative pentobarbital used in Texas executions.

Ladd was convicted of killing 38-year-old Vicki Ann Garner and setting fire to her body at her Tyler apartment in 1996. He was on parole at the time after pleading guilty to a triple slaying in Dallas.