An Oklahoma inmate has died following an abandoned execution attempt. Clayton Lockett, 38, was declared unconscious 10 minutes after he was injected with the first drug of a new cocktail, but was writhing at 16 minutes. Although the execution was halted, Lockett died of an apparent heart attack within the hour. States are struggling to find effective execution drugs as European manufacturers refuse to supply the traditional ones. The incident — which coincides with a study suggesting as many as four percent of those on death row may be innocent — is sure to reignite controversy over the death penalty.