A story from The Nation here:
Executioners injected drugs into the corpses of death penalty convicts for “disposal purposes,” according to documents obtained by the Independent. Oklahoma prison officials say it is protocol to inject the remaining drugs of a three-drug cocktail when inmates overdose on the first drug, an anesthetic. But a former pathologist says this practice could distort postmortem toxicology results, hindering medical examiners from determining the level of pain experienced during an execution.
That last part speaks for itself, among the macabre hypocrisies of “measuring” pain.