The state Supreme Court late Sunday refused to grant a stay of execution for convicted killer Stanley "Tookie" Williams, meaning the founder of the Crips gang will be executed early Tuesday unless Gov. Arnold Schwarzenegger (R) grants clemency or a last-ditch federal appeal succeeds.

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

The new witness's statements were sent to Schwarzenegger's office. Aides said the governor would not announce his decision on the clemency request before Monday.

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.

The state's high court ruled 6 to 0 against staying the execution, saying Williams's last-minute appeal lacked merit and was untimely. Deputy Attorney General 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. He denies committing the murders but has apologized for founding the Crips.