The California Supreme Court has rejected a late appeal to reopen the case of condemned Crips gang leader Stanley Tookie Williams.
Mr Williams (51) is due be executed at 12.01 am tomorrow for murdering four people in two 1979 robberies around Los Angeles.
The court's decision means his fate is now in the hands of Governor Arnold Schwarzenegger.
His supporters had hoped the anti-gang books for children he wrote in prison would help him win clemency from Mr Schwarzenegger, but they now appear dispirited that the celebrity governor has waited until the last day to announce his decision.
Pondering their fifth habeas corpus petition on the case over the past quarter century, the state Supreme Court last night rejected his lawyers' effort - filed a day before - to reopen the case.
In recent weeks, Mr Williams' supporters had argued he was a life worth sparing because his message inspires inner-city youth. The inmate was subject of a film staring Academy Award winner Jamie Foxx.
"I see that as cruel," Barbara Becnel, who edited Williams's anti-gang books, told a news conference when asked about the delayed word from Mr Schwarzenegger.
Prosecutors also expect last-minute appeals to other courts before the scheduled execution by lethal injection at San Quentin State Prison.
Death penalty opponents were expected to gather at San Quentin on the bay north of San Francisco later today. Los Angeles civic and community leaders, worried that Mr Williams' execution could spark rioting, have urged the public to remain calm whatever the governor decides.
Mr Williams has openly spoken of a brutal gang past for which he apologises.