California - United States authorities on Tuesday executed Stanley "Tookie" Williams, a convicted killer who was at the centre of one of biggest anti-death penalty campaigns in the United States in decades, a spokesperson for San Quentin prison said.

Williams, executed by lethal injection, was declared dead at 12:35, she added.

Several thousand people gathered outside the prison, on the shores of the Pacific Ocean south of San Francisco, raising their voices in anger when Williams' execution was announced.

"It's over, but it's not," said Reverend Jesse Jackson, one of several well known personalities who supported Williams in his quest to have his execution stayed.

"He came in without any kind of resistance, was strapped down, showed no kind of resistance whatsoever," said Los Angeles Times reporter Steve Lopez, who witnessed the execution along with nearly 40 other people, including supporters of Williams and the families of his victims.

Williams, 51, was found guilty in 1981 of four murders, those of a convenience store clerk and a family of Chinese immigrants.

He had admitted being a founder of the brutal Crips gang that terrorised Los Angeles at the time but denied the killings. While on death row he renounced his violent past and wrote acclaimed books to try to persuade youths not to join gangs.

Hollywood stars and civil rights activists had joined an international campaign to try to save Williams' life. But all court appeals were rejected and California governor Arnold Schwarzenegger turned down his clemency bid on Monday.

"Clemency cases are always difficult and this one is no exception," Schwarzenegger said in a statement.

"After studying the evidence, searching the history, listening to the arguments and wrestling with the profound consequences, I could find no justification for granting clemency.

"The facts do not justify overturning the jury's verdict or the decisions of the courts in this case," the governor added.

• Click here forn Stanley "Tookie" Williams case information

California - Seventeen reporters witnessed the execution of convicted killer and gang leader Stanley "Tookie" Williams and gave their accounts afterward, reports CNN.

The process of inserting the IVs to administer the lethal chemicals took about 20 minutes, with staff having particular difficulty getting a needle into Williams' left arm.

Crystal Carreon of the Sacramento Bee newspaper said Williams was restless during the preparations - a sentiment echoed by San Quentin State Prison Warden Steven Ornoski.

"He did seemed frustrated that it didn't go as quickly as he thought it might," Ornoski.

A crowd of demonstrators began gathering outside the gates of the prison early on Monday evening, with celebrities, activists and anti-death-penalty advocates pleading for Williams' life to be spared.

"I am saddened that we are continuing to demean human life by pretending that we are God and making determinations to kill other individuals for what it is claimed they have done," former M*A*S*H star and death penalty opponent Mike Farrell told CNN.

The execution process began at 12:01 in the execution chamber at San Quentin - 34 minutes later, prison officials confirmed Williams had died.

The announcement of Williams' death was punctuated in the witness gallery by three of his invited supporters, who shouted in unison, "The state of Californian just killed an innocent man," as they exited.

Minutes earlier in the gallery, reporters said at least one of the three had given Williams a raised fist salute.

The execution went ahead as scheduled after the United States Supreme Court late Monday rejected a last-ditch appeal.

The high court's ruling followed California Governor Arnold Schwarzenegger's decision to deny clemency for Williams.

Before Williams went to the execution chamber, the stepmother of one of the men Williams was convicted of killing said she felt "justice is going to be done tonight."

Williams had maintained his innocence since his arrest and conviction in the brutal 1979 slayings. He had denounced gang violence and written children's books with an anti-gang message, donating the proceeds to anti-gang community groups.

As Williams was being moved to a holding cell next to the death chamber Monday evening, his lead attorney, John Harris, had said the convict was "at peace."

Protesters for and against the death penalty gathered outside the gates of San Quentin early on Monday evening.

Williams was sentenced to death in 1981 in the killing of Owens, a 26-year-old Los Angeles convenience store clerk, in February 1979. The clerk was shot twice in the back with a 12-gauge shotgun while face-down on the floor.

Less than two weeks later, jurors concluded, Williams killed an immigrant Chinese couple and their 41-year-old daughter while stealing less than $100 in cash from their motel. Part of the daughter's head was blown off in the shooting.

• Click here forn Stanley "Tookie" Williams case information

SAN QUENTIN, Calif.   Convicted killer Stanley Tookie Williams , the Crips gang co-founder whose case stirred a national debate about capital punishment versus the possibility of redemption, was executed Tuesday morning.

Williams, 51, died at 12:35 a.m. Officials at San Quentin State Prison seemed to have trouble injecting the lethal mixture into his muscular arm.

As they struggled to find a vein, Williams looked up repeatedly and appeared frustrated, shaking his head at supporters and other witnesses.

"You doing that right?" it sounded as if he asked one of the men with a needle.

After he was declared dead, his supporters shouted in unison: "The state of California just killed an innocent man," as they walked out of the chamber.

The case became the state's highest-profile execution in decades. Hollywood stars and capital punishment foes argued that Williams' sentence should be commuted to life in prison because he had made amends by writing children's books about the dangers of gangs and violence.

In the days leading up to the execution, state and federal courts refused to reopen his case. Monday, Gov. Arnold Schwarzenegger denied Williams' request for clemency, suggesting that his supposed change of heart was not genuine because he had not shown any real remorse for the killings committed by the Crips.

"Is Williams' redemption complete and sincere, or is it just a hollow promise?" Schwarzenegger wrote. "Without an apology and atonement for these senseless and brutal killings, there can be no redemption."

Williams was condemned in 1981 for gunning down convenience store clerk Albert Owens, 26, at a 7-Eleven in Whittier and killing Yen-I Yang, 76, Tsai-Shai Chen Yang, 63, and the couple's daughter Yu-Chin Yang Lin, 43, at the Los Angeles motel they owned. Williams claimed he was innocent.

Witnesses at the trial said he boasted about the killings, stating "You should have heard the way he sounded when I shot him."

Williams then made a growling noise and laughed for five to six minutes, according to the transcript that the governor referenced in his denial of clemency.

About 1,000 death penalty opponents and a few death penalty supporters gathered outside the prison to await the execution. Singer Joan Baez, M*A*S*H actor Mike Farrell and the Rev. Jesse Jackson were among the celebrities who protested the execution.

"Tonight is planned, efficient, calculated, antiseptic, cold-blooded murder and I think everyone who is here is here to try to enlist the morality and soul of this country," said Baez, who sang "Swing Low, Sweet Chariot" on a small plywood stage set up just outside the gates.

A contingent of 40 people who had walked the approximately 25 miles from San Francisco held signs calling for an end to "state-sponsored murder."

But others, including Debbie Lynch, 52, of Milpitas, said they wanted to honor the victims.

"If he admitted to it, the governor might have had a reason to spare his life," Lynch said.

Former Crips member Donald Archie, 51, was among those attending a candlelight vigil outside a federal building in Los Angeles. He said he would work to spread Williams' anti-gang message.

"The work ain't going to stop," said Archie, who said he was known as "Sweetback" as a young Crips member. "Tookie's body might lay down, but his spirit ain't going nowhere. I want everyone to know that, the spirit lives."

Among the celebrities who took up Williams' cause were Jamie Foxx, who played the gang leader in a cable movie about Williams; rapper Snoop Dogg, himself a former Crip; Sister Helen Prejean, the nun depicted in "Dead Man Walking"; and Bianca Jagger.

During Williams' 24 years on death row, a Swiss legislator, college professors and others nominated him for the Nobel Prizes in peace and literature.

"There is no part of me that existed then that exists now," Williams said recently during an interview with The Associated Press.

"I haven't had a lot of joy in my life. But in here," he said, pointing to his heart, "I'm happy. I am peaceful in here. I am joyful in here."

Williams' statements did not sway some relatives of his victims, including Lora Owens, Albert Owens' stepmother. In the days before his death, she was among the outspoken advocates who argued the execution should go forward.

"[Williams] chose to shoot Albert in the back twice. He didn't do anything to deserve it. He begged for his life," she said during a recent interview. "He shot him not once, but twice in the back. ... I believe Williams needs to get the punishment he was given when he was tried and sentenced."

SAN FRANCISCO, Dec. 13 - Stanley Tookie Wiliams, a condemned gangster whose execution drew more national and international attention than any here in decades, was executed by lethal injection and pronounced dead at 12:35 this morning at San Quentin State Prison.

Delois N. Blakely, an activist from Harlem, was among the demonstrators who gathered outside San Quentin prison to protest the execution of Stanley Tookie Williams.

Mr. Williams, 51, a co-founder and leader of the Crips gang of Los Angeles who was convicted of the brutal murders of four people in 1979 amid an avalanche of gang violence there, had become, to his supporters, an icon of jailhouse redemption and a powerful critic from his cell on death row and through his writings of the perils and misguided allure of the gang life on the nation's urban streets.

Outside the gates of San Quentin, an estimated 1,000 people held a largely peaceful vigil, reading aloud from Mr. Williams's books, with some, shortly after midnight Monday, shouting, "Long live Tookie Williams!" At 12:38 a.m., three minutes after Mr. Williams was pronounced dead - after a process that took 36 minutes and 15 seconds from the time Mr. Williams was brought into the chamber - the crowd sang "We Shall Overcome."

Gov. Arnold Schwarzenegger on Monday rejected arguments that Mr. Williams was either innocent of capital murder or deserving of mercy because of his claims of redemption, and denied a clemency petition to commute his sentence to life in prison. Late Monday, Mr. Schwarzenegger also turned down a request from the defense for a stay of execution based on a last-minute claim of innocence citing new accounts from witnesses.

And at about 11:30 p.m. Monday, the governor rejected a second request for a 60-day reprieve, a legal appeal that prison officials said slightly delayed the start of the execution, originally scheduled for 12:01.

Among the 39 witnesses - including journalists, victims' relatives, Mr. Williams's lawyers and supporters and prison officials - several of the journalists who said they had witnessed other executions described the lethal injection procedure as unusually long, as a nurse struggled to insert a needle in Mr. Williams's muscular left arm for about 12 minutes. Mr. Williams, who was strapped to what looked like a tilted-back dental chair inside the sea-foam green death chamber, appeared frustrated, witnesses, including the prison warden, said.

Several times he lifted his head from the gurney to look up at his supporters, some of who were blowing kisses, and he was mouthing "I love you," the witnesses said.

The prison warden, Steve Ornoski, said the execution was not unusually drawn out, although he did say he noticed that Mr. Williams, who appeared to be trying to help his executioners during the process, seemed exasperated.

"It depends on the person's veins and whether they are readily accessible," Mr. Ornoski said. "And also it's a high pressure assignment for someone that's in front of so many people."

Mr. Williams, who was among 651 death row inmates at San Quentin, today became the 12th man executed in the state since California reinstated the death penalty in 1978.

Death row inmate Stanley Tookie Williams sits in a visiting cell at San Quentin prison.

While witnesses are expected to be silent during an execution, when Mr. Williams was pronounced dead, three of the five witnesses he asked to watch him die shouted, "The state of California just killed an innocent man!"

Lora Owens, the stepmother of Albert Owens, a 26-year-old clerk at a Los Angeles 7-11 whom Mr. Williams was convicted of killing at point blank range with a sawed off shotgun, was stoic as she watched the execution, witnesses said. But after the outburst from Mr. Williams's supporters, Ms. Owens, who said earlier that the execution would finally bring justice to her stepson, broke down in tears, the witnesses said.

Besides the governor's refusal to spare his life, Mr. Williams had suffered two other setbacks Monday, as first a federal appeals court and then the Supreme Court ruled against granting a stay of execution.

In his decision denying clemency, issued less than 12 hours before Mr. Williams was scheduled to die, Mr. Schwarzenegger wrote that the case had been appealed to various courts since Mr. Williams was condemned in 1981, each one upholding his conviction.

The governor described the four murders in chilling detail, cited a long list of the evidence against Mr. Williams, and said the proof of his guilt was "strong and compelling."

Gov. Arnold Schwarzenegger denied clemency for the Crips co-founder.

"I told him the clemency had been rejected," Mr. Jackson said in a telephone interview as he was leaving the prison late Monday evening. "He kind of grimaced and then he smiled and said, 'We will not give up hope.' "

The clemency request was based on what lawyers for Mr. Williams said was evidence of his dramatic turnaround in prison, where Mr. Williams became a vocal critic of gang violence, speaking out through children's books, lectures and memoirs. One memoir was the basis for a 2004 television film, "Redemption," staring Jamie Foxx, one of the many celebrities, including rap star Snoop Dogg, and activists who rushed to join the effort to save Mr. Williams's life in recent weeks.

"Our petition for clemency was based on Stanley Williams's personal redemption, his good works and positive impact that those works have had on thousands and thousands of kids across this country and on Williams's ability to continue to do those good works going forward," Jonathan Harris, one of his lawyers, said at a news conference in Sacramento on Monday.

"I have spent many an hour with Stanley Williams," Mr. Harris said, "and I refuse to accept that Stanley Williams's redemption is not genuine." He said the defense team had failed to persuade the governor to meet with Mr. Williams.

In his decision, the governor cited a planned escape by Mr. Williams while he was awaiting trial that involved his "blowing up a jail transportation bus and killing the deputies guarding the bus" as an example of behavior that is "consistent with guilt, not innocence." He also said there was no evidence that Mr. Williams's speaking out against gang violence had any effect on "the continued pervasiveness of gang violence" in crime-ridden neighborhoods.

Alice Huffman, president of the California State Conference of the N.A.A.C.P., joined Mr. Harris at the news conference and said the governor's decision to allow the execution to go forward was politically motivated. It comes at a time when he is under fire from his own party for appointing a Democrat as his new chief of staff and after the defeat of four ballot measures he supported during a special election in November.

But the governor's office declined to elaborate on his decision to deny clemency.

Polls show that a majority of Californians supports the death penalty.

As Mr. Williams's supporters rallied around the state Monday and Tuesday, with no reports of violence, as some had feared, from police, others said he deserved to be executed.

The Rev. Jesse Jackson, in front of San Quentin State Prison Monday, was among those who fought for clemency for Mr. Williams.

Before leaving for San Quentin to witness the execution, Ms. Owens told CNN: "I'm just glad that we're almost to the end of this. I'm glad that finally Albert is going to have the justice he deserves."

In South Los Angeles, where the Crips have been blamed for hundreds of killings, several residents said they believed that if Mr. Williams was guilty, he should be put to death.

"If he'd have killed your daughter, you'd want him dead," said Lee Johnson, 89, a retired construction worker. "He killed somebody. You got to pay for what you do."

At San Quentin at 6 p.m. Monday, officials moved Mr. Williams into what is known as the "death watch cell," a 6-by-8-foot enclosure with a toilet and a sink about 15 feet from the execution chamber. They said he was searched, given a change of clothes - blue denim jeans and a blue T-shirt - and a stack of 50 to 75 letters from friends, school children and others.

Over the next few hours, he watched some television in a guarded adjacent cell but spent most of the time on the telephone with lawyers and supporters, discussing their failed last-ditch efforts to have the governor intervene, the officials said.

Mr. Williams decided in the final hours to allow five personal witnesses to his death, the number to which he was entitled, including Barbara Becnel, his longtime friend and advocate, who will take possession of his body but who did not yet release details of funeral arrangements.

Mr. Jackson said he had tried to persuade Mr. Williams to have witnesses there, saying to him, "You need to leave with a look in the face of the people who love you and not a look in the face of the executioners. You need to have witnesses. When it's over, your friends can tell your story."

Mr. Williams did not request a last meal, although he ate oatmeal earlier in the day Monday and drank water and milk throughout the day and evening, prison officials said.

In an interview with the New York Times at the prison on Nov. 29, Mr. Williams said of the traditional last rite, "I'd be out of my mind to accept a meal from a place that wants to destroy me."

Mr. Williams's supporters and lawyers who had seen him in recent days said he was at peace with his imminent death.

But, in the Times interview he said: "To threaten me with death does not accomplish the means of the criminal justice system or satiate those who think my death or my demise will be a closure for them. Their loved ones will not rise up from the grave and love them. I wish they could. I sympathize or empathize with everyone who has lost a loved one. But I didn't do it. My death would not mollify them."

Of the execution, he said: "I'll go through it with dignity, with integrity, with love and bliss in my heart. I smile at everything, and I'm quite sure I'll smile then, too."