FARGO, N.D. (AP) - The FBI is investigating whether convicted murderer and sex offender Joseph Edward Duncan III might be involved in the slaying of a Montana teenager found dead in North Dakota four years ago.

"We're a long way from saying he's a suspect, but it's certainly a case we're reviewing," said Donald Robinson, an FBI supervisor in Coeur d'Alene, Idaho.

Russell Turcotte, of Wolf Point, Mont., was 19 when he disappeared in July 2002. He called his mother from Grand Forks, and she promised to wire him money so he could take the bus home. His body was found in a tree grove along U.S. Highway 2 near Devils Lake the following November.

Duncan, 43, who was living in Fargo when Turcotte disappeared, pleaded guilty last month to murder and kidnapping in Idaho, in a deal that leaves him still eligible for the death penalty. He was charged in state court with bludgeoning a man, a woman and a teenager to death at a home near Coeur d'Alene in 2005 so he could kidnap the woman's two youngest children for sex.

Federal authorities are expected to charge Duncan in the abduction of the children and the killing of one of them, a 9-year-old boy.

Authorities say Duncan, a Tacoma, Wash., native, spent most of his adult life in Washington prisons for sex crimes against children. He also is being investigated in the slayings of two children in Washington and one in California.

Bill Turcotte said his family asked the FBI last year whether Duncan might be a suspect in his son's death.

Robinson said the FBI is putting together a timeline on Duncan's whereabouts dating back to the early 1990s.

"Every single day Mr. Duncan was out of custody, we're looking at where he was - and we're looking at all sorts of unsolved crimes," Robinson said.

"There is no direct evidence Mr. Duncan was involved in the disappearance of Mr. Turcotte," Robinson said. "Mr. Duncan was in North Dakota at that time."

Bill Turcotte said the FBI told him there is evidence placing Duncan at the same Grand Forks truck stop "within hours" of the time Russell Turcotte was last seen.

Robinson said he could not comment on "anything that may or may not be evidence."

Bill Turcotte said investigators were skeptical of any possible connection because his son was 19 and Duncan preyed on children.

"Russell was very young in appearance and he was also very vulnerable," Bill Turcotte said. "He was traveling alone and was looking for help, so maybe he reached out for the first person who offered him a hand and it was the wrong person."