The US state of Missouri plans to execute on Tuesday a man sentenced to death for the 2004 killing of his girlfriend and her three children, an act that he denies.

Leonard Taylor, a 58-year-old man, is scheduled to receive a lethal injection in the Potosi penitentiary in the US Midwest.

He was sentenced to death in 2008 for the murders of Angela Rowe and her three children, aged 10, six and five years.

They were found dead, each with a bullet in the head, in their house on December 3, 2004. According to the forensic doctors, they had been dead for several days.

Taylor has always maintained that they were still alive on November 26, when he left the Jennings, Missouri, home and flew to California.

At the trial, prosecutors said he confessed to the murders to his brother and made his gun disappear in front of a witness, and jurors found him guilty.

Since then, he has made numerous attempts to clear his name -- all unsuccessful.

Also on Monday, Missouri Governor Mike Parson rejected his request for clemency.

"The evidence shows Taylor committed these atrocities and a jury found him guilty. Courts have consistently upheld Taylor's convictions," the Republican governor said in a statement.

The Innocence Project, which fights against miscarriages of justice and defends Taylor, claims that the brother's testimony was obtained under duress and that he later recanted.

His lawyers have recently introduced the testimony of his daughter who swears that her father was in California with her at the time of the murders, without succeeding in obtaining a reopening of the file.

They have filed a final appeal Tuesday to the US Supreme Court, which is expected to rule quickly.

If it does not stay the execution, Taylor will be the fifth death row inmate executed since January 1 in the United States.