Late on Monday, the Nevada State Supreme Court agreed to a request by the American Civil Liberties Union of Nevada to stay the execution pending an upcoming ruling by the U.S. Supreme Court on the constitutionality of execution by lethal injection. The country's highest court agreed on September 25 to review the issue, the same day Castillo was scheduled to die.

The Nevada court also said the state's methods are cruel and unusual because the prisoner is so heavily sedated it is impossible for witnesses to determine the actual effects of the injection, effectively violating First Amendment rights.

The ruling is an effective reprieve because Castillo's execution order is only good for a week, and the U.S. Supreme Court is not expected to rule before then. A number of states, including California, have halted executions pending the legal review of whether the current method of lethal injection constitutes cruel and unusual punishment.

Castillo had given up his remaining appeals, saying he was ready to die for bludgeoning an 86-year-old Las Vegas teacher to death in 1995.

Castillo worked on Isabel Brendt's roof, then returned with a female companion after finding a house key. He burglarized the home and beat Brendt to death with a tire iron. They later burned down the home.