(CNN) A difficult execution in Alabama this week is raising well-tread questions about the humanity and appropriateness of lethal injections.

Smith's execution had been delayed twice, and his legal team had tried to delay it a third time, saying that Alabama's drug protocol would cause him to suffer, violating the Constitution's ban on cruel and unusual punishment.

Lethal injection has long inspired debate: How reliable is it in delivering quick, painless death? What drugs are necessary to ensure such an end?

There are several botched executions that serve as benchmarks in America's long and uncomfortable history with lethal injections. Here are some of them.

JUST WATCHED Joseph Wood: Execution takes two hours, 15 injections Replay More Videos ... MUST WATCH Joseph Wood: Execution takes two hours, 15 injections 01:45