Miami, Florida - A Gulf War veteran convicted of killing his girlfriend and her three young children is to be executed by lethal injection in Florida on Thursday.

Jeffrey Hutchinson (62) is to be put to death for the murders of Renee Flaherty (32) and her children – Geoffrey (9), Amanda (7), and Logan (4).

Hutchinson's lawyers claim he suffers from mental illness as a result of his experiences during the 1990-1991 Gulf War, but appeals to halt his execution have been rejected.

According to court documents, Hutchinson argued with Flaherty on the evening of September 11, 1998, packed his clothes and guns into his truck, and went to a bar.

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He then returned home and fatally shot Flaherty and her children with a 12-gauge shotgun.

Following the murders, Hutchinson called 911 and said, "I just shot my family."

When sheriff's deputies arrived, they found Hutchinson dazed on the floor of the garage with blood on his clothes and gunshot residue on his hands. The phone was still connected to the 911 dispatcher.

Hutchinson claimed at trial that the murders were carried out by two masked and armed intruders who shot Flaherty and the children and then fled.

The execution is to be carried out at 6:00 PM ET at the Florida state prison in Raiford.

There have been 14 executions in the US this year: 10 by lethal injection; two by firing squad; and two using nitrogen gas.