EDITORIAL NOTE: Edward Eugene Harper was captured on July 24, 2009.

It's been 14 years since Edward Eugene Harper allegedly assaulted two young girls in Mississippi, and he's still on the run.

But the hunt for Harper, who treated his young wife and alleged victims as “things,” according to one investigator, recently received a huge boost from federal authorities.

Harper, 62, is the latest addition to the FBI’s Ten Most Wanted Fugitives . A former truck driver who now may be working as a ranch hand in Montana, he is being sought in the 1994 assaults of two girls in Hernando, Miss., and for unlawful flight to avoid prosecution.

FBI officials are offering $100,000 for information leading to his arrest. He is believed to pose a serious threat to children.

Harper’s behavior toward his wife and young victims — one of whom looked up to Harper enough to call him “Daddy” — went “above and beyond” even most sexual predators, FBI Special Agent Ryan Arton said.

“The psychological abuse was unbelievable,” Arton told FOXNews.com. “He looked at these people as things, not human, by the way he manipulated and controlled them.”

While living in a rural campsite in DeSoto County, Miss., Harper, who was 47 at the time, and his then-19-year-old wife began to look after one of his alleged victims, a 3-year-old girl, after her homeless mother could no longer care for her, Arton said.

Harper began molesting the toddler within a month, investigators said.

“This girl looked up to him so much in the beginning that she called him Uncle Eddie or Daddy,” Arton said. “Her mom basically dumped her off and then he took advantage of that.”

Officials said the second young victim was an 8-year-old girl who lived in the neighborhood.

Arton said Harper “constantly threatened” his wife and young victims with violence if they ever told anyone of the abuse.

“He knew he had the trust of these little girls and his wife, and he played on that,” Arton said. “He used that to his advantage and he gradually introduced other things that brought him to the level of sexually molesting them.”

“It was just unbelievable," Arton said. "I mean, no remorse with his sexual perversion.”

The girls finally came forward in March 1994, Arton said, seven months after the alleged sexual abuse began. Harper was indicted on April 27, 1994, and released on bond.

He failed to appear for a scheduled court hearing six months later, and he has eluded authorities ever since. Officials assume he has adopted multiple identities or has been living as a survivalist.

Harper repeatedly told his wife he subscribed to Sovereign Citizen ideology and was "aligned" with the Montana Freemen, a group involved with domestic terrorism activities, according to the FBI. Although authorities have never been able to confirm his affiliation with the group, Harper did live in Montana prior to his second marriage.

"We do know that he was out there," Arton said. "[But] when the guy took off, he took off. That was it.”

Four years later, in 1998, Harper’s mother died. He had a “special relationship” with his mother, Arton said, and he called his half-sister in Arkansas to tell her about their mother's death. During that conversation, which is the last known contact Harper has had with his relatives, Harper told his half-sister that he was working with cattle and sheep, but he gave no details to his whereabouts.

“He was very careful not to reveal his location,” Arton said. “He didn’t provide any information whatsoever.”

But Harper’s half-sister did give authorities a tip: Shortly after their conversation, Arton said, Harper’s half-sister went through their mother’s belongings and found letters from Harper using the alias Ed Harmon. According to the letters, “Ed Harmon” had been working on ranches in Montana and Wyoming.

“We don’t believe they were in contact besides that call,” Arton said.

Arton said he believes Harper, a father of two who has had little formal education, continues to work as a laborer.

"I can't see him going through any formal procedure to get employment," he said. "I could see him doing manual labor such as ranching work and stuff like that where he's getting paid in cash. There's no doubt he's doing that."

Harper was diagnosed with schizotypal personality disorder by a behavioral psychologist in Mississippi shortly after his 1994 arrest. According to the American Psychiatric Association, the disorder is characterized by a desire for social isolation, social anxiety and odd behavior.

Arton said Harper was described as loner, but he "could distinguish right from wrong and is fully capable of knowing what he did and be able to stand trial."

Harper last month became the 491st fugitive to be placed on the FBI's Ten Most Wanted Fugitives list. Authorities hope the additional exposure will lead to his arrest.

He is white, 5-foot-10 and 165 pounds, with gray/brown hair, hazel eyes and a medium complexion. He is considered dangerous.

"We can't predict exactly what he's going to do, but a lot of times that type of behavior continues. It's not like they commit one particular crime and then they're done with it," Arton said. "This is a pattern, this is sexual perversion. He's going to be a danger to small children, especially if he's alone with them."

Click here to see the FBI's Ten Most Wanted Fugitives description of Edward Eugene Harper.