In 2013, witnesses reported Florida inmate William Happ did not close his eyes for 10 minutes after the drug was administered and then began moving his head.

In January, Ohio inmate Dennis McGuire's death took more than 25 minutes. Witnesses said McGuire was gasping and snorting during the process.

The same Massachusetts expert touted in Oklahoma by Attorney General Scott Pruitt  Dr. Mark Dershwitz  had testified in Ohio that McGuire wouldn't feel pain and possibly would feel "euphoria."

A 2008 case known as Baze v. Rees prompted the U.S. Supreme Court's most significant ruling regarding lethal injection protocol in recent years. The justices ruled that Kentucky could legally execute the inmate in that case but stated plainly: If the first of three drugs failed to render an inmate unconscious, it was "uncontested" there was a "substantial, constitutionally unacceptable risk" of suffocation and pain from the two drugs that followed.

Due to what state officials deemed a "collapsed vein" or failed IV insertion, no one knows yet how much midazolam Lockett received.

At least 10 minutes after the drug had supposedly rendered him unconscious, Lockett was able to speak, lift his head and shoulders off the gurney and he writhed for three minutes, according to witnesses.