As if the twisted saga of Joseph Edward Duncan III (search) were not horrific enough, there is a growing fear that the registered sex offender may have additional young victims in multiple states.

Police around the country are taking a closer look at unsolved killings for a possible connection to Duncan, who is accused of killing three people in their Coeur d'Alene (search)-area home in order to abduct two children for sex.

Duncan, 42, was arrested early July 2 at a restaurant after a waitress found him with one of the children, 8-year-old Shasta Groene (search). Remains of Shasta's 9-year-old brother, Dylan, were found in a Montana forest two days later.

Authorities have confirmed they are looking at Duncan as a potential suspect in four additional deaths, and Kootenai County Sheriff's Detective Brad Maskell said numerous other law enforcement agencies have made inquiries.

Duncan was 16 in 1980 when he was sentenced to 20 years in prison for raping a 14-year-old boy at gunpoint. He spent all but eight of the subsequent 25 years in prison.

After his arrest last month, authorities say Duncan talked about three children who were killed while he was paroled between 1994 and 1997 and living in Seattle.

One, Anthony Martinez, 10, was forced into a car in the southern California town of Beaumont in April 1997 as his friends watched. Sixteen days later a forest ranger found the boy's nude, bound body.

A few days before Martinez' disappearance, Duncan tested positive for marijuana — a parole violation — stole his girlfriend's car and disappeared, reportedly to southern California. Investigators have taken a renewed look at the case, and they now say his partial fingerprint has been found on duct tape used to bind the boy.

"We're pretty confident that he's our suspect," Riverside County Sheriff Bob Doyle said earlier this month.

Also this month, police in Oak Harbor, Wash., said they were investigating the possibility that Duncan was linked to the death of Deborah Palmer, 7, who disappeared on March 27, 1997, while walking to school. Her body was found four days later — the same day Duncan stole his girlfriend's car.

Duncan has also discussed the earlier killings of two half-sisters in the Seattle area, although authorities there said he did not confess and they have found no physical evidence linking Duncan to the deaths.

Carmen Cubias, 9, and Sammiejo White, 11, were kidnapped from a motel in Seattle in July 1996. Their remains were found 17 months later.

Duncan was finally arrested Aug. 27, 1997, at the home of his half-sister in Kansas City, Mo., on the parole violation. He was released from prison again in 2000 and enrolled to study computing in Fargo, N.D.

Registered as a sex offender there, Duncan indicated in his Web log that he chafed under the scrutiny of law enforcement officers. He traveled widely, visiting friends and relatives as far away as Florida, and taking trips throughout the Midwest.

In July 2004, Duncan was arrested for allegedly molesting a 6-year-old boy and attempting to molest another boy at a playground in Detroit Lakes, Minn. He jumped bail this April.

According to testimony from Shasta Groene, Duncan told her he spotted her and her brother playing outside their home in mid-May; on May 15, he came for them, wearing night vision goggles and carrying a rifle as he entered the house, authorities say.

According to the charges against him, Duncan bound and then used a hammer to beat to death Brenda Groene, her 13-year-old son Slade and her boyfriend Mark McKenzie.

Then, police say, he took Shasta and Dylan to a campsite in Montana, where Shasta told authorities he repeatedly molested the children and killed Dylan.

While it is The Associated Press' policy not to identify alleged victims of sexual assault in most cases, the search for Shasta and her brother was heavily publicized and their names are widely known.

Duncan is jailed without bail on three charges of first-degree murder.

The FBI has not released a list of Duncan's movements during his stints outside prison, but amateur Internet sleuths have pored through his Web site and court and other public records, creating their own timeline.

One site called "The Cellar" includes a map that shows the places Duncan is known to have visited since his first conviction in 1980 — 11 states, most in the West or Midwest. The Web site lists slain or missing children from areas Duncan has visited since 2000, though there is no indication Duncan is tied to those crimes.