Washington state's Supreme Court has lifted the stay of execution for a death row inmate who claimed the state's method of lethal injection violated constitutional bans on cruel and unusual punishment.

The high court unanimously ruled Thursday that Cal Coburn Brown's claims are moot because the state Department of Corrections changed its method of execution earlier this year from a three-drug cocktail to a one-drug system.

The court issued a stay last year just hours before Brown was set to die for torturing and killing a Burien woman in 1991. The state can now reschedule the execution, but the earliest it could happen is September.