MOUNT VERNON, Wash. -- Prosecutors have charged a man with first-degree murder in the slaying of a substitute teacher and assistant track coach at Ferndale High School who reportedly was involved in a "swinger" lifestyle that included the defendant's wife.

Kenneth McBride, who lived in Skagit County when Jeremy Scully was shot to death in April 2008, was arrested Wednesday at his home in Lebanon, Ore.

Scully disappeared while driving from his Bellingham apartment to a friend's house in Alger on April 25, 2008.

His body was found last April 27 by hikers on Blanchard Mountain in northwest Skagit County, and an autopsy showed he was shot to death.

Skagit County detectives served a search warrant at the home of McBride and his wife, Venessa, after Scully's body was found. They seized several firearms, among other items.

Court documents say Scully left his Bellingham apartment to go to Alger to help Kenneth McBride fix the McBrides' roof. Venessa McBride was having an affair with Scully, with her husband's knowledge, according to the documents.

But her husband reportedly told her at one point he would become "unglued" if Scully interfered with their relationship.

She told deputies that on the day Scully disappeared, her husband called and asked her to pick him up near a trailhead near the Skagit-Whatcom County line within a mile or two of where Scully's Nissan Sentra was found, according to the court records.

She added that when she arrived home, no work had been done on the roof and there was no sign of Scully.

Scully's body was found three days later.

Court documents say Venessa McBride gave birth to a child in January 2009. The documents say April 2008, when the child would have been conceived, was a period when she had sexual encounters only with Kenneth McBride and Scully, and Kenneth McBride had undergone a vasectomy.

At a news conference where the arrest was announced, Skagit County Chief Deputy Will Reichardt released few details and did not discuss the suspected motive .

"We believe without a doubt that he is the person guilty of this, and I think the motive will become very clear as the case progresses," he said.

Reichardt said the investigation was complex and investigators had to wait for results from complex forensic tests and computer analysis of evidence.

Scully coached pole vault at Ferndale High School for eight years. He also worked as a substitute teacher at the school and helped coach pole vaulting at Western Washington University.