The bodies of an Oregon mother and her 3-year-old son have been found more than a month after they vanished, hidden in a forest where the boy's father cut wood, authorities said Monday.

"Really good detective work" led authorities to find the bodies of Karissa and Billy Fretwell on Saturday in a heavily wooded area northwest of the state capital of Salem, Yamhill County District Attorney Brad Berry said.

Michael John Wolfe, the child's father, was arrested last month at a doughnut shop in Portland and has been charged with kidnapping and aggravated murder in their deaths.

An autopsy found 25-year-old Karissa Fretwell died of a single gunshot to the head, while additional testing this week will determine how Billy died, prosecutors said.

Fretwell hadn't been heard from since May 13. Her family reported her and her son missing a few days later when she didn't show up for work.

Court papers show Fretwell went to court last year to establish that Wolfe is Billy's father and had filed a petition seeking over $1,000 a month in child support.

Wolfe, 52, had a permit to cut wood close to where the bodies were found, Berry said.

"I can't tell you how the information came about," the district attorney said of pinpointing the location. "I can tell you Wolfe was familiar with this area."

Searchers who were part of a crew of dozens from different agencies found the bodies after looking for about two hours Saturday. The bodies had been covered with debris, Berry said.

Searchers had combed the area previously to no avail.

A firearm also has been found, but prosecutors said detectives don't know yet if it's the gun used to kill Fretwell.

Wolfe is jailed without bail and scheduled to appear in court later this week. It wasn't immediately known if he has a lawyer.

A stuffed animal and vases of fresh flowers have appeared on the hood of Fretwell's car near her Salem apartment, KPTV-TV reported.

"I was hoping that they'd come home," neighbor Sara Vangilder said. "I didn't want to think the worst."