"I don't need this court," Patrick Drum, 34, of Sequim, told Clallam County Superior Court Judge Ken Williams. "I'm guilty. I want to plead guilty."
The judge told Drum that under state law, he could not yet accept that plea, the Peninsula Daily News reported.
Williams noted County Prosecutor Deb Kelly has said she's considering whether to seek the death penalty. She has another 30 days from Wednesday's arraignment to make that decision.
Aggravated murder is punishable in Washington by either death or life in prison without parole.
Gary Lee Blanton Jr. and Jerry W. Ray were killed in separate shootings earlier this month. The county sheriff has said a signed note Drum left in a rental car said he hated sex offenders and "it had to be done."
Drum's attempted plea surprised both Kelly and Drum's court-appointed lawyer, Karen Unger.
"I don't recall ever having a murder defendant try to plead guilty at an arraignment," said Kelly, who has worked in the county prosecutor's office for 22 years.
Drum told Williams he wanted to represent himself. He said the same thing at an earlier hearing to a different judge, but that judge appointed Unger to represent him. Unger said Drum had not told her about his plan to plead guilty.
A probable cause statement from the sheriff's office, filed earlier with the court, said Drum had stated he planned to drive to nearby Jefferson County and kill another sex offender there.
"He had obtained names with research he had done with a computer," sheriff's detective Sgt. Lyman Moores said Wednesday.
Investigators say Drum shot Blanton, 28, on the night of June 2 at a home Drum was renting. Blanton was renting a room in the home.
Drum then drove to Ray's home a few miles away where Ray, 56, was killed early on June 3, Sheriff Bill Benedict has said.
For some reason, Drum abandoned a rental car he had been driving and was seen on foot in the remote area of the northern Olympic Peninsula. Reports of a suspicious man in the area brought deputies, who found the car and the note inside that led to the victims and identified Drum as a suspect. Drum was arrested later on June 3.
State Corrections Department records show Drum has served time for convictions that include burglary and drug possession.