(Updates with execution, details)
By Bill Cotterell
TALLAHASSEE, Fla., Jan 7 (Reuters) - A Florida man who spent nearly 40 years on death row for killing a Miami couple and later stabbing a prison guard to death with a sharpened spoon was executed on Tuesday, a state prison official said.
Askari Abdullah Muhammad, 62, who was known as Thomas Knight when he killed his former employer and his wife in 1974, was pronounced dead at 6:45 p.m. EDT (2345 GMT) from a lethal injection, said Misty Cash, a spokeswoman for the Florida Department of Corrections.
Muhammad won a stay of execution last month after he legally challenged the use of a sedative, midazolam hydrochloride, as the first in a series of three drugs used for lethal injections in Florida.
The state switched to midazolam last year when makers of another sedative, pentobarbital, refused to supply it to states using the drug in executions.
Attorneys for Muhammad said the new drug was an ineffective sedative and caused inmates to suffer pain when the subsequent two drugs - a paralytic agent and heart-stopping drug - were administered to complete the injection process.
A Florida circuit judge ruled, however, there was insufficient evidence of pain in two previous executions carried out with midazolam last year.
Muhammad was sentenced to death for the 1974 murders of Sydney and Lillian Gans in Miami. Muhammad had previously worked for Gans at a paper bag company, and abducted him from a parking lot with a rifle, forcing Gans to drive home and get his wife before making them withdraw $50,000 from a bank.
He shot the couple in the back of their heads and fled but was captured a short time later.
Muhammad escaped while awaiting trial and was implicated in the fatal shooting of a liquor store clerk in October 1974 in Cordele, Georgia. He was not charged in that case but was returned to Florida for trial in the Gans murders.
In 1980, while on death row, Muhammad stabbed correctional officer Richard Burke while being escorted to a shower room. Three years later, he was sentenced to die for Burke's killing.
Muhammad made a final appeal in late December, arguing that the state withheld evidence of his mental condition that might have disputed premeditation in the slaying of the prison guard.
The state's highest court rejected that appeal without comment on Monday. (Editing by Kevin Gray, G Crosse and Steve Orlofsky)