HUNTSVILLE, Texas - A Texas death row inmate is asking the federal courts to keep him from being executed for the 1999 slaying of his ex-girlfriend while he already was on parole for killing his estranged wife.

William Rayford, 64, would be the nation's second inmate executed this year, both in Texas.

Rayford is facing lethal injection Tuesday evening for beating, stabbing and strangling 44-year-old Carol Lynn Thomas Hall, whose body was found about 300 feet (91 metres) inside a drainage pipe behind her home in South Dallas' Oak Cliff area. Hall's 11-year-old son also was stabbed in the attack but survived to testify against Rayford.

Rayford's lawyers are seeking to have his punishment halted. In their argument before the U.S. Supreme Court, they said his death sentence was tainted because his attorney at his trial in 2000 improperly introduced the subject of race as a factor in prison violence while questioning a prison expert during the punishment phase. Nadia Wood, a Dallas-based federal public defender, told the high court that in bringing it up the trial lawyer implied "that people like Mr. Rayford - a black man - are the cause of the violence."

An assistant Texas attorney general, Jefferson Clendenin, disputed the argument, telling the justices the witness never testified as an expert in rates of violence because he wasn't qualified to do so and that none of the witness' trial testimony "even implied that African-Americans are more likely than others to be violent or that Rayford himself was a future danger."

Rayford's lawyers argued in a separate appeal to a lower federal court that earlier a federal court improperly denied money for his appeals and that Hall's slaying may not have qualified for a capital murder charge. They also argued that Rayford suffered from brain damage from lead poisoning because he grew up near a toxic site and carried lead residue from old gunshot wounds.

Evidence "more than established" Rayford kidnapped Hall while trying to kill her, supporting the capital murder charge, and arguments about lead poisoning were based on a "vague, general and nebulous conclusion" by a defence expert, Clendenin indicated in his response.

Hall, who knew Rayford since they both grew up in a Dallas housing project, had broken up with him two months earlier, according to evidence in the case. Rayford entered her home on Nov. 16, 1999, using a key she didn't know he had. They argued and it turned violent.

Hall's son, Benjamin, testified at Rayford's trial that he suffered a punctured lung from the stab wound, was hit on the head when he tried to protect his mother, and watched her run from the home with Rayford pursuing her. He said he saw Rayford carry his mother toward the drainage pipe where her body eventually was found.

Police responding to a call about the attack arrested Rayford at the scene. Hall's blood was on his face and clothing. He told an officer Hall could be found "in the hole ... up in the sewer, in the water."

Rayford was convicted of murder in 1986 for fatally stabbing his estranged wife, Gail Rayford, in front of their four children. She had obtained a court order four days earlier to keep him away.

He was sentenced to 23 years in prison for her slaying but was paroled after eight years under a former Texas law that allowed some prisoners to be released as the state struggled with prison crowding. He had been on parole for five years when Hall was killed. Relatives said she was aware of his previous murder conviction when they became a couple and believed it was her Christian duty to give people second chances.

Another Texas prisoner is set to die Thursday. John David Battaglia, 62, of Dallas, is to be executed for the May 2001 shooting deaths of his daughters, ages 6 and 9.