Prosecutors asked the California Supreme Court on Sunday to reject former gang leader and convicted killer Stanley Tookie Williams' request to block his execution, set for early Tuesday.

The request "is without merit and is manifestly designed for delay," Deputy Attorney General Lisa Brault wrote.

Brault's brief came hours after a lawyer for Williams urged the court to issue a stay of execution on the grounds that Williams should have been allowed to argue at his 1981 trial that someone else killed one of his four alleged victims. The defense also noted state lawmakers are expected to consider a moratorium on the death penalty next month.

The justices didn't immediately rule. They earlier denied defense attorney Verna Wefald's request to reopen the case because of allegations that shoddy forensics linked a weapon used in three of the 1979 murders to a shotgun registered to Williams.

Williams has also appealed to Gov. Arnold Schwarzenegger for clemency, and the governor said last week that he was agonizing over the case.

Williams, who co-founded the Crips street gang, has spoken out against violence during his 24 years at San Quentin and has written children's books on the evils of gang life. His supporters say he has redeemed himself and that to execute him would send the wrong message.

Clemency has been rare in California, though. Schwarzenegger denied the only two previous clemency requests to cross his desk. The last California governor to grant clemency was Ronald Reagan, who spared a mentally ill killer in 1967.

Williams, 51, was convicted of killing a man during a robbery in February 1979 and of murdering a couple and their daughter at a South Los Angeles motel in March 1979.

He denies committing the murders but has apologized for founding the Crips, a gang prosecutors blamed for thousands of murders in Los Angeles and beyond.

In the petition to the state's highest court late Saturday, Wefald told the justices that Los Angeles County prosecutors failed to disclose at trial that witness Alfred Coward was not a U.S. citizen and that he had a violent criminal history. Coward is now in prison in Canada for the murder of a man during a robbery.

"All of the witnesses who implicated Williams were criminals who were given significant incentives to testify against him and ongoing benefits for their testimony," Wefald wrote.

The California Supreme Court, a federal district court judge in Los Angeles, the 9th U.S. Circuit Court of Appeals and the U.S. Supreme Court have all upheld Williams' convictions.