A lawyer for convicted murderer and co-founder of the Crips street gang Stanley Tookie Williams, who is scheduled to be put to death Tuesday, is asking the California Supreme Court to stay his execution.

Pasadena Attorney Verna Wefald also filed a 150-page petition Saturday challenging the validity of the four convictions and death sentences meted out to Williams in 1981, the Los Angeles Times reported.

Williams has been the subject of a celebrity-studded clemency campaign -- including Archbishop Desmond Tutu and Oscar-winning actor Jamie Foxx -- based on a claim that he has redeemed himself with anti-gang work from death row.

Williams has written nine anti-gang books aimed at young people, been nominated several times for the Nobel Peace and Literature Prize, and his "Protocol for Street Peace" has been used by rival gangs to broker gang truces.

Williams was convicted of killing a man during a robbery in February 1979. Williams also was convicted of the March 1979 murders of a couple and their daughter at a South Los Angeles motel.

Williams has consistently denied he committed the murders, although he has apologized for his role as a co-founder of the Crips, a gang considered responsible for numerous murders in Los Angeles and beyond.

Williams, 51, is scheduled to die by lethal injection at San Quentin State Prison on Tuesday.

However, California Gov. Arnold Schwarzenegger's office is currently weighing the request for clemency.

On Saturday, Schwarzenegger's office said that the governor had not made a decision.

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

The petition filed Saturday night alleges that an "error of constitutional magnitude led to a trial that was so fundamentally unfair absent the error no reasonable judge or jury would have convicted" him.

Wefald argues that prosecutors failed to disclose at trial that witness Alfred Coward was not a U.S. citizen and that he had a violent criminal history. depriving Williams of the opportunity to argue Coward was the killer in the February 1979 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 in the stay petition.

"This type of testimony is the leading cause of wrongful convictions in murder and capital cases in the United States," she wrote, citing a study done at the Northwestern University Law School's Center on Wrongful Convictions.

Wefald also alleged that the prosecution failed to make known that Williams was "forcibly, involuntarily, surreptitiously and continually drugged with powerful tranquilizers and/or other psychotropic medication by the Los Angeles County jail as a form of management control, thus rendering him incompetent to stand trial."

Fearing a repeat of the 1992 race riots in which 52 people died, police, schools and community groups have been told to prepare for violence if clemency is not granted.

Robin Toma, executive director of the Los Angeles County Human Relations Commission, said the organization had received "credible" threats of violence if Williams is put to death.

There are also fears that Williams' execution could cause unrest in the prison system.

For that reason, all prisoners at San Quentin will be locked down during the execution, and there is the expectation that other state prisons will choose to do the same.

A California governor has not granted clemency since 1967, when Ronald Reagan spared the life of a brain-damaged killer.