CARSON CITY, Nev. – The state Supreme Court has lifted its stay of an execution order following a decision by the American Civil Liberties Union of Nevada to drop its challenge of the use of lethal injections to execute inmates.

The high court's brief order on Tuesday followed the ACLU's recent dropping of a case involving William Castillo, convicted of murder and sentenced to death in the 1995 slaying of a retired Las Vegas school teacher.

However, Castillo has an appeal pending in U.S. District Court, and his execution can't be scheduled until the federal appeal is resolved.

Lee Rowland of the ACLU of Nevada has said the ACLU decided to drop its state Supreme Court case and the attorney general's office went along with the move. Rowland added that the U.S. Supreme Court has “basically blessed” lethal injections as a method of execution and the state Supreme Court likely would agree with the nation's highest court.

The U.S. Supreme Court ruled in April that lethal injections, when done properly, don't violated Eighth Amendments protections against cruel and unusual punishment. To stop an injection, the court said defense lawyers must prove “substantial risk of serious harm.”

Thirty-five of 36 death penalty states use lethal injection. Legal fights cover myriad battlefronts – from attacking the medical qualifications of those administering the drugs to questions about whether the chemicals used comply with controlled substances laws.

All lethal injection states use some kind of triple-dose procedure that first delivers an anesthetic to put the inmate to sleep, then a second paralyzing chemical, and a final dose that stops the heart.