California Governor Arnold Schwarzenegger had been asked to grant clemency in the case but declined to do so.

Former gang leader Stanley Williams was sentenced to death in 1981 for a total of four murders carried out in 1979. While on death row Stanley Williams completely transformed himself, repudiating his past acts and violent lifestyle and dedicating himself to educating young people about the dangers of gang life.

Amnesty International UK Director Kate Allen said:

“This is yet another sad milestone in the history of the US justice system.

“Tookie Williams’ violent past was well known but he had become a textbook version of rehabilitation and his execution was a travesty of justice.”

Stanley Williams, one of the founders of the notorious "Crips" street gang in Los Angeles, California in the early 1970s underwent what he describes as a "redemptive transition" in prison, renouncing gang life and working to educate young people about its dangers.

Since coming out of solitary confinement, his behaviour record in prison had been exemplary.

He wrote a series of Children's rights's books about the dangers of gang life, was nominated for a Nobel Peace Prize on several occasions, and in 2005 received a US presidential service award from the President's Council on Service and Civic Participation.

Stanley Williams had also always maintained his innocence of the crimes for which he was executed.

According to his clemency petition, the case against him rested on testimony from accomplices in the crime and informants who were facing imprisonment or the death penalty for various offences, but who all received reduced sentences or freedom in exchange for their testimony.

There were also concerns about racial discrimination within the trial process itself.

Williams was tried in an area where only one per cent of the jury pool was black. The trial prosecutor removed all Afro-Americans from the jury and on one occasion compared Williams - who sometimes appeared in court in shackles - to a Bengal tiger.

In January 2005 California Governor Arnold Schwarzenegger announced plans to remodel the focus of the prison system away from punishment towards rehabilitation.

In its 2004 ruling, the California Ninth Circuit Court of Appeal said that Stanley Williams’ "good works and accomplishments since incarceration may make him a worthy candidate" for an act of executive clemency.

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