Stanley Tookie Williams maintained his innocence right up until his death, even when an admission of guilt may have spared him execution. Even after the courts and Gov. Arnold Schwarzenegger rejected a flurry of Williams' last-ditch appeals before his execution early Tuesday, his supporters vowed to prove his innocence. Williams, the Crips gang co-founder whose case stirred a national debate about capital punishment versus the possibility of redemption, was executed Tuesday morning for killing four people in 1979. 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. Lora Owens, stepmother of one of the four people Williams was convicted of killing witnessed the execution. "I believe it was a just punishment long overdue," she told ABC's "Good Morning America." Williams' case became one of the nation's biggest death-row cause celebres in decades, with Hollywood stars and capital punishment foes arguing 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. His execution also drew fierce criticism in Europe, where politicians in Schwarzenegger's native Austria called for his name to be removed from a sports stadium in his hometown. "Schwarzenegger has a lot of muscles, but apparently not much heart," said Julien Dray, spokesman for the Socialist Party in France, where the death penalty was abolished in 1981. Williams became the 12th person executed in California since lawmakers reinstated the death penalty in 1977. 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." Schwarzenegger said the evidence of Williams' guilt was "strong and compelling." Witnesses at Williams' trial said he boasted about the killings, saying: "You should have heard the way he sounded when I shot him." 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. Williams was led into the death chamber at midnight, shackled and handcuffed. He declined to give a formal final statement. He seemed frustrated by the length of time it took officials to insert the intravenous lines in his arms. He repeatedly looked up, shaking his head at supporters, reporters and other witnesses whom officials did not identify. In all, it took nearly a half-hour to prepare Williams for execution. It took much less time to die; he appeared to stop breathing just moments after a prison official read the death warrant and said, "The execution shall now proceed." Williams was described as "complacent, quiet and thoughtful," by Corrections Department spokeswoman Terry Thornton in the hours before the execution. He declined to have a last meal as he waited in the holding cell, drinking milk instead. Prison officials said he spent his last hours reading mail, watching television and visiting with his lawyers and friends. After watching her longtime friend die, Barbara Becnel told the crowd of hundreds gathered outside prison gates that she would prove Williams' innocence and that Schwarzenegger was a "cold-blooded murderer." She said Williams "was brave and strong and he was everything we believed him to be."