A death row inmate in Oklahoma suffered a prolonged execution after the lethal injection failed to work as expected.<br /><br />Clayton Lockett, 38 suffered a vein collapse, which prevented the cocktail of three drugs from taking their full effect. <br /><br />The execution was halted and prison officials pulled the curtain across to prevent witnesses seeing Lockett’s discomfort.<br /><br />The law demands witnesses are present to see the sentence carried out:<br /><br />“At he was still lifting his shoulders and head grimacing. And he appeared to be in distress,“said one.<br /><br />“So from 6:23, the execution started. 6:39 is when they closed the curtains on us. A 16-minute process to watch,” recounted another.<br /><br />Lockett eventually died of a heart attack.<br /><br />Charles Warner was due to be put to death two hours latter in the same room, but following the controversy his execution has been postponed for 14 days.<br /><br />Oklahoma Governor Mary Fallin said the states’ execution procedurers are to be reviewed.<br /><br />Lockett was sentenced to death for the shooting of a 19-year-old woman in 1999. Warner was convicted of the rape and murder of an 11-month-old girl in 1997.<br /><br />The two men previously challenged the state to reveal the names of the companies that supply the lethal drugs, which is forbidden under law. <br /><br />Oklahoma says the law is necessary to protect suppliers from harassment and legal action.