Gov. Jay Nixon denied clemency early Wednesday morning for inmate Paul Goodwin, hours after the U.S. Supreme Court also turned down two petitions that sought to halt his execution.

The announcement from Nixon's office came several minutes after the 12:01 a.m. Wednesday scheduled time for the lethal injection.

Goodwin, 48, was executed soon after. He was convicted of killing 63-year-old Joan Crotts inside her St. Louis County home in 1998.

This undated file photo provided by the Georgia Department of Corrections shows convicted murderer Robert Wayne Holsey. A jury in February 1997 convicted Holsey of killing Baldwin County sheriff's deputy Will Robinson. (Georgia Department of Corrections/The Associated Press)

An appeal to the U.S. Supreme Court and a clemency petition both claimed that Goodwin is mentally disabled, making him ineligible for the death penalty. The Supreme Court declined to halt the execution, without comment.

The court also denied a second petition that questioned Missouri's use of an execution drug purchased from an undisclosed compounding pharmacy.

Goodwin's attorney, Jennifer Herndon, said his IQ has been tested at 73. His sister, Mary Mifflin, wrote in a statement that her brother remains child-like, even in prison. She said the death penalty "is not a just punishment for his crime — an act that occurred out of passion, not premeditation, by a man with the mental capabilities of a child, not an adult."

The Missouri Attorney General's office responded to the Supreme Court petition by citing testimony at Goodwin's trial, where a psychologist testified that Goodwin's IQ is low, but not low enough to be considered mentally disabled.

Alcohol a factor in fatal attack

Goodwin received special education as a child but still failed several grades, Mifflin wrote. He relied on relatives and his girlfriend to help with such tasks as buying groceries or paying bills, she said.

When the girlfriend died, Goodwin wasn't capable of handling the grief and turned to alcohol, which was a factor in his attack on Crotts, Mifflin wrote.

Goodwin is sorry for the crime, Herndon said.

"From the beginning he's said, `This is horrible.' But he's so impaired he doesn't really have the ability to show remorse like a normal adult would show," she said.

But Crotts' daughter, Debbie Decker, told the St. Louis Post-Dispatch that Goodwin deserves no mercy.

"I've been sitting back waiting for this to happen," Decker said. "I'm hoping all these bad memories will go away."

In the mid-1990s, Goodwin lived in a St. Louis County boarding house that was next door to where Crotts, a widow, lived. The two had been involved in several verbal confrontations.

Goodwin was evicted in 1996 after he and friends harassed Crotts, including throwing beer cans into her yard. Court records show that Goodwin blamed Crotts for his eviction, telling her, "I'm going to get you for this," according to trial testimony.

On March 1, 1998, Goodwin, 6-foot-7 and roughly 300 pounds, entered Crotts's home and confronted her. After a sexual assault, he pushed her down the basement stairs before striking her head several times with a hammer. She died at a hospital.

U.S. Supreme Court denies Georgia inmate's appeal

Police found a handwritten note on Crotts's kitchen table that read, "You are next." Fingerprints from the note and a Pepsi can matched Goodwin's, and his hearing aid was also found inside the home. He admitted the crime after his arrest.

The execution is the 10th in Missouri this year — the most ever for the state. It would also tie Texas for the most executions in any state in 2014. Texas, Missouri and Florida have combined for 27 of the 33 executions in the U.S. this year.

Georgia, meanwhile, executed a death-row inmate convicted of murdering a sheriff's deputy after a convenience store robbery in 1995, the state attorney general said in a statement.

Robert Wayne Holsey, 49, was put to death by lethal injection at 10:51 p.m. ET on Tuesday night, state Attorney General Sam Olens said in a statement.

Holsey's attorneys had argued his execution should be halted because he was mentally disabled and received inadequate representation from a lawyer who drank heavily at the time of his trial, but the U.S. Supreme Court denied their request for a stay of execution.