A California judge has upheld the death sentence of Horace Edwards Kelly in the first case tried under a recent Supreme Court ruling that allows mentally retarded inmates to challenge their execution sentence.

The case will now go to the state's high court. Riverside County Judge W. Charles Morgan ruled this week that Kelly's attorneys failed to prove that Kelly was mentally retarded when he killed three people in 1984, including an 11-year-old boy, the Los Angeles Times reported.

The state's high court ruled in February 2005 that inmates could receive a hearing to challenge their death penalties if an expert said they were retarded. Kelly's attorneys argued their client displayed significant mental deterioration and suffered from schizophrenia.

Morgan said he doubted the credibility of the defense witnesses and asked why lawyers did not cite a deteriorating mental status in Kelly's previous trials, The Times reported.

Kelly, who has twice come within a week of execution but was awarded stays, will have the case heard in the state's high court, Riverside County Chief Deputy District Attorney Kevin Ruddy said.