Hundreds of people waited outside California's San Quentin prison for the execution of ex-gang leader Stanley "Tookie" Williams.
Emotions were high as campaigners for and against the death penalty held their vigil.
Ex-gang members were among those who pleaded with California Governor Arnold Schwarzenegger for clemency.
Williams' supporters called his execution "state-sponsored murder", saying he had made amends through the anti-gang children's books he wrote in jail.
Pro-death penalty campaigners argued Williams, convicted of four murders 24 years ago, should die by lethal injection because of his lack of remorse.
US civil rights leader Jesse Jackson was among a number of high-profile figures to support Williams in his plea for a stay of execution.
Rev Jackson said Williams had accepted the news that his bid had failed "with a certain strength, a certain resolve".
Mr Schwarzenegger said Williams' insistence he was innocent and refusal to apologise or atone meant the death penalty was the only option.
Journalists who witnessed the lethal injection said the mood in the execution chamber was sombre. Supporters of Williams and relatives of his victims watched him die.