A hitchhiker convicted of stabbing to death a driver who offered to take him to Denver will remain on death row, the Utah Supreme Court has decided.

In a unanimous decision released Monday, the court rejected the appeals of Joseph Mitchell Parsons. Parsons pleaded guilty to first-degree murder in 1987 and was given the death penalty by a jury.The court rejected Parsons' argument that it is unconstitutional for state law to define a killing committed by someone previously convicted of a violent crime as first-degree murder. Parsons' attorney said his client was thus being punished twice for his earlier crimes.

But the decision, written by Associate Chief Justice Richard C. Howe, said Parsons should have raised that objection before he pleaded guilty.

"One cannot voluntarily waive his right to trial and then seek relief on grounds that the trial, if it had occurred, may have been constitutionally flawed," Howe wrote.

The court rejected several other pleas, including one that it was improper for former Iron County District Judge Harlan Burns to attend part of the sentencing hearing to lend moral support to his son, the prosecutor. The presiding judge, J. Philip Eves, noted Burns was a spectator and welcomed him to the court.

Justices said Parsons failed to show that Burns' presence caused any harm.

Parsons pleaded guilty to stabbing to death Richard L. Ernest near a highway rest area in Iron County. Ernest had offered Parsons a ride earlier in the day near Barstow, Calif.