The only logical conclusion is there was gross negligence here

"The execution has underscored the ineffective protocol that was adopted in August," said Martin McClain, an attorney and death penalty critic who has handled scores of death penalty cases.

Under the protocol, the inmate is given sodium pentothal to render him unconscious. Next, pancuronium bromide is given to paralyze the lungs. Potassium chloride is then injected to stop the heart, but is said to be painful as it works its way through the circulatory system.

Reporters for Florida media and an attorney representing death row inmates witnessed the execution and described a scene in which Diaz appeared to thrash and medical personnel were called in to administer more drugs.

"During the time Mr. Diaz appeared to be speaking, it was my observation that he was in pain," Neal Dupree of Capital Collateral Regional Counsel testified in the petition. "His face was contorted and he grimaced on several occasions. His Adam's apple bobbed up and down continually, and his jaw was clenched."

Critics say state officials were aware of Diaz's liver condition and should have modified the procedure to ensure Diaz would be unconscious when the third drug was given.

"It's clear they inflicted pain on him, and it's clear that they knew ahead of time about his condition," McClain said. "The only logical conclusion is there was gross negligence here."