That thing we do up in Starke
In all likelihood, Diaz remained conscious as the drugs pooled in his arms and the pancuronium bromide began to paralyze him. Diaz would have become chemically locked in—that is, mentally aware but without control of any voluntary muscles—and he would have starved for air as his diaphragm shut down and he slowly suffocated. In the autopsy report, the medical examiner noted "bilateral venous jugular distention"—an abnormal swelling of both jugular veins in Diaz's neck that could be a sign he struggled for air.
Witnesses to the execution reported Diaz moved throughout the procedure, suggesting he was awake and trying to overcome the onset of paralysis. Chris Tisch, a St. Petersburg Times reporter who witnessed the execution, wrote that Diaz immediately began grimacing and appeared to speak at the start (his words could not be heard by the witnesses because a glass window separates the death chamber from the viewing room). He repeatedly squinted his eyes and lifted his chin. Ten minutes into the execution—around the time he was expected to die—he turned his head to the right and began to cough. Sixteen minutes into the execution, he was still moving his mouth and chin. By the twenty-second minute, he appeared to have stopped moving—but then two minutes later his body "jolted," according to Tisch, and his eyes opened more widely. At 6:34, a doctor checked Diaz’s vital signs. He or she left the execution chamber, returned a minute later, checked again, and at 6:36 an execution team member pronounced Diaz dead.
Tisch wrote in his notes that for several minutes Diaz's mouth was "flexing like a fish out of water"—a sign he was struggling for air. Ron Word, an Associated Press reporter, also witnessed the execution. Afterwards, he wrote: "It seemed like Angel Nieves Diaz would never die."