America’s Supreme Court has agreed to review Oklahoma’s controversial method of execution by lethal injection.<br /><br /> It is taking up a case brought by three death row inmates, who accuse the state of violating the US Constitution’s ban on cruel and unusual punishment.<br /><br /> The three-drug process used by Oklahoma prison officials has been in the spotlight since a botched execution last year. Clayton Lockett could be seen twisting after staff failed to place the IV correctly.<br /><br /> The inmates challenging the state’s procedure argue that the sedative used, midazolam, cannot achieve the level of unconsciousness required for surgery and is therefore unsuitable for executions.