Published: Mar 19, 2014 2:53 PM EDT

MIAMI (AP) - A man convicted of killing two female co-workers by beating them with a hammer and setting them on fire is scheduled for execution Thursday at Florida State Prison in Starke.
    
Robert L. Henry, 55, was sentenced to die for the November 1987 slayings of Phyllis Harris, 53, and 35-year-old Janet Thermidor, with whom he worked at the Cloth World store in Deerfield Beach. After the attacks, he stole $1,269 from the store.
    
Although Henry at first told police the crime was committed by an unknown assailant, Thermidor lived long enough to positively identify him as the perpetrator in a recorded statement to investigators. Broward State Attorney Michael Satz, who prosecuted the 1988 trial, told the jury that Henry had committed one of the most cold-blooded acts in recent memory.
    
"You talk about atrocious, heinous, cruel, vile or wicked. He literally burned them up," Satz said then. "This is a case that nightmares are made of."
    
Barring a successful last-minute appeal, Henry is scheduled to die by injection at 6 p.m. Thursday. The Florida Supreme Court last week rejected his most recent appeals, including yet another challenge to the state's method of lethal injection. Henry would be the fourth person executed in Florida this year.
    
In his latest appeal to the U.S. Supreme Court, Henry's lawyers cite medical experts who claim that one of the drugs used in Florida's lethal injection procedure, midazolam, could cause a heart attack and extreme pain, because Henry suffers from coronary artery disease, high blood pressure and high cholesterol levels. His lawyers seek a stay of execution so those issues can be sorted out, citing the Eighth Amendment's prohibition against cruel and unusual punishment.
    
In response, the Florida attorney general's office said there is no requirement for a hearing for each inmate who claims he might suffer some level of pain in the execution process. They also noted that five death row inmates have been executed "without any mishap" using the newer drug combination.
    
"Avoidance of all pain is not demanded by the Constitution," the state lawyers wrote.
    
According to trial testimony and his own statements to police, Henry first approached Harris after the store had closed on Nov. 2, 1987, telling her unknown robbers had ordered him to tie her up and blindfold her. Henry took Harris to a restroom, tied her to a urinal, then went to the store's office where he hit Thermidor repeatedly on the head with hammer, doused her with a flammable liquid and set her on fire.
    
Henry then went back to the restroom and attacked Harris with the hammer, setting her ablaze as well.
    
Authorities responding to the fire found Harris dead but Thermidor still alive, after she had tried to douse the flames in a second restroom. She lived about 12 hours, and her statement pointed to Henry. He was arrested the next day.
    
"I don't know why he had to do that to me. He didn't have to do that to me," Thermidor said on the tape, which was played in court during Henry's trial.
    
Court records show that Henry initially claimed the robbery was committed by three masked intruders who also abducted him, but later he confessed to acting alone. That confession was also recorded.
    
He was convicted of two counts of first-degree murder, armed robbery and arson, largely on the strength of Thermidor's deathbed statement.
    
"If ever I have seen a classic case of a dying declaration, this is it," Satz said at the trial. He declined to comment recently, citing Henry's appeals.
    
Henry's lawyer tried unsuccessfully to persuade jurors that Thermidor never said on the tape that she actually saw Henry and that police had improperly coerced his confession.
    
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