(Reuters) - A man convicted of killing his wife and her 5-year-old son nearly 30 years ago was executed at Florida State Prison on Wednesday, the third person to die by lethal injection in 24 hours across the U.S. South.

John R. Henry's death was the third U.S. execution since a botched injection in Oklahoma in April renewed a national debate over capital punishment.

Henry, 63, who previously served seven years for manslaughter in the slaying of his common-law wife, was pronounced dead at 7:43 p.m. He asked forgiveness of his victims' families and Jesus Christ in a brief final statement, the state Department of Corrections said.

Henry's attorneys sought to have him declared mentally unfit for execution, but the U.S. Supreme Court rejected his last round of appeals.

Henry met with relatives and a Catholic spiritual adviser before declining his last meal on Wednesday, according to Jessica Cary, spokeswoman for the corrections department.

He was condemned for fatally stabbing his wife, Suzanne Henry, at her home in Zephyrhills a few days before Christmas 1985. He then abducted her son by a previous relationship, Eugene Christian, and stabbed the boy to death with the same knife several hours later.

Two convicted killers, one in Georgia and the other in Missouri, were put to death less than a day earlier.

Georgia inmate Marcus Wellons, 58, convicted of the 1989 rape and strangulation of a 15-year-old neighbor he abducted while she was walking to her school bus stop, was executed on Tuesday night by injection. The procedure went smoothly, a state corrections official said.

A little more than an hour later at a state prison in Missouri, John Winfield, 46, met the same fate for killing two women and leaving his ex-girlfriend blind and disfigured in a 1996 rampage.

The cases of Wellons and Winfield were the first executions since killer and rapist Clayton Lockett died on April 29 in a mishandled execution in Oklahoma that sparked an uproar among death penalty opponents.

Lockett suffered an apparent heart attack and died about 30 minutes after prison officials halted his execution because of problems administering the injection. A preliminary autopsy released by his lawyers last week showed the state failed to properly insert an intravenous line to deliver the fatal dose of medication.

Henry's death brought the number of executions in the United States this year to 23.