Virginia Gov. Terry McAuliffe (D) said Monday he will not intervene before the scheduled execution of convicted Fairfax County murderer Alfredo R. Prieto, meaning a stay from the U.S. Supreme Court is Prieto’s last hope before he faces lethal injection on Thursday night.

Prieto, 49, was sentenced to two death sentences in December 2010 for the slayings of Rachael A. Raver and Warren H. Fulton III, both 22, who were shot 22 years earlier in a vacant lot outside of Reston. Evidence of a third Northern Virginia slaying, of Veronica “Tina” Jefferson in Arlington in May 1988, was also presented to the jury during its sentencing phases.

Authorities believe Prieto is responsible for nine killings between 1988 and 1990, when he was arrested in Ontario, Calif., for the rape and murder of 15-year-old Yvette Woodruff. He was sentenced to death for that case in 1992, but his California appeals are still continuing.

So when a DNA databank in 2005 linked Prieto to the three Northern Virginia slayings from 1988, prosecutors in Fairfax and Arlington extradited him to Virginia. During trials in Fairfax in 2007 and 2008, defense lawyers presented evidence that Prieto’s IQ fell below the state standard for mental retardation. Prosecutors presented evidence showing he was above the standard, and two juries convicted him of capital murder.

With Prieto’s appeals nearly exhausted, McAuliffe said Monday that he had thoroughly reviewed the facts and legal proceedings of the case, and “I have decided not to intervene in this execution. Mr. Prieto was convicted in a fair and impartial trial, and a jury sentenced him to death in accordance with Virginia law. Federal and state appellate courts have extensively reviewed his case and denied his requested relief.”

In a statement, McAuliffe added, “It is the Governor’s responsibility to ensure that the laws of the Commonwealth are properly carried out unless circumstances merit a stay or commutation of the sentence. After extensive review and deliberation, I have found no such circumstances, and have thus decided that this execution will move forward. I will continue to pray for all of the individuals and families affected by these tragic and horrible crimes.”

In Prieto’s first Fairfax trial in 2007, a jury rejected the mental retardation defense and convicted Prieto of capital murder and rape. But during the sentencing phase, a juror rebelled, refused to continue deliberating and a mistrial was declared. At a second trial in 2008, the jury again rejected the retardation defense, convicted Prieto and voted for two death sentences, which Fairfax Circuit Court Judge Randy I. Bellows imposed. But the sentences themselves, not the guilty verdict, were reversed on appeal. A third trial for sentencing only was held in 2010, and the defense did not raise retardation as an issue. The jury again voted for two death sentences, which Bellows imposed in December 2010.

Prosecutors said Prieto shot Fulton in the back while he was on his knees, then shot Raver in the back as she ran, and raped her as she lay dying. Jefferson was also raped before being shot. The two episodes were first linked by DNA in 2000, and then connected to Prieto when his DNA was entered into a national database in 2005.

“What you did to those two young people,” Bellows told Prieto, “was vile and horrible and beyond the pale. What I do today, in my view, is impose a just sentence.”