San Francisco ? The state Supreme Court late Sunday refused to grant a stay of execution for gang member and convicted killer Stanley Tookie Williams, meaning Williams will be executed early Tuesday unless the governor grants clemency or a last-ditch federal appeal succeeds.

Williams’ supporters made another pitch to save his life earlier Sunday, telling Gov. Arnold Schwarzenegger’s staff that they had a new witness who could help prove Williams’ innocence.

“All we need now is time to investigate to make sure this story is real,” said NAACP California President Alice Huffman. “We’re hoping and praying for clemency, but we’re not going to leave any stone unturned.”

The new witness’s statements were sent to Schwarzenegger’s office, where the staff said the governor wouldn’t announce his decision on the clemency request before today.

Williams, 51, is scheduled for execution at 12:01 a.m. Tuesday for the deaths of four people in 1979. He would be the 12th inmate executed by the state since California reinstated the death penalty in 1977.

A guard watches the gates of San Quentin State Prison Sunday in San Quentin, Calif. Stanley Tookie Williams, co-founder of the Crips gang and a convicted murderer, is scheduled to die by lethal injection at the prison early Tuesday.

The state’s high court ruled 6-0 against staying the execution, saying Williams’ last-minute appeal lacked merit and was untimely. Deputy Atty. Gen. Lisa Brault had implored the justices early Sunday to dismiss his petition, writing that it “is without merit and is manifestly designed for delay.”

The justices earlier denied a defense request to reopen the case over allegations that shoddy forensics linked a weapon used in three of the 1979 murders to a shotgun registered to Williams.

Williams founded Los Angeles’ violent Crips street gang, but his supporters say he has turned his life around and redeemed himself by speaking out against violence and writing children’s books on the evils of gang life during his 24 years at San Quentin prison.

He was condemned for the murder of a man during a robbery in February 1979 and the slayings of a couple and their daughter at a South Los Angeles motel the following month.

He denies committing the murders but has apologized for founding the Crips, a gang prosecutors blamed for thousands of murders in Los Angeles and beyond.