Witness in Fugitive Polygamist Case Speaks Out

The crux of the FBI's case against one of its Top 10 Most Wanted fugitives rests on the shoulders of a 20-year-old Colorado woman who is reluctant to testify but spoke exclusively to ABC News about her case.

When Candi Shapley was just 16, she was forced into an abusive polygamist marriage arranged by Warren Jeffs, a self-proclaimed prophet and leader of the Fundamentalist Church of Jesus Christ of Latter Day Saints. Jeffs has been on the run since 2004, accused of sexual conduct with a minor and conspiracy to conduct sexual conduct with a minor. Yet, despite numerous allegations of forcing minors into sex, Shapley is the only victim who has gone on the record even though she said she is not angry at Jeffs.

"They're not going after Randy for raping me, they're going after Warren for marrying us," Shapley told ABC News in her first public interview. "He's on the 10 Most Wanted List with Osama bin Laden. I think that's unfair. I'm not for Warren Jeffs, but I'm not against him."

In March 2002, Shapley was summoned to a Nevada hotel where she was surprised that her father and Jeffs had arranged her marriage to Randolph Barlow, a 28-year-old man she had never met.

"We just walked in right in front of Warren Jeffs and we were getting married," Shapley said.

Within hours of her wedding, Shapley found herself sharing a two-bedroom double-wide trailer with Barlow, his first wife and their four children.

"You're going into another family," Shapley said. "He has another wife and children. They do things a certain way."

Shapley described her life as lonely and said Barlow forced her to have sex.

"One time he held me down, ripped my clothes off, held his hand over my mouth so I couldn't scream," Shapley said. "That was because I told him I didn't want to have children, that I was too young."

After 18 months, Shapley sought drastic measures to get out of her marriage.

"Finally I decided the only way out was ... to have an affair," she said.

Shapley said committing adultery was a horrific sin in the church community, and she knew it would ensure her ouster from the religious sect.

When she broke the news of her infidelity to her parents, they begged her to stay, but Shapley, who was pregnant with her lover's twins, decided to go.

"I don't even know if I'd be alive right now if I hadn't gotten out," Shapley said.

Today, Shapley is at the center of the case authorities are building against Jeffs. Despite numerous allegations of forcing minors into sex, Shapley is the only victim who has gone on the record.

Now she said she is focusing on raising and protecting her twin daughters.

"I don't want them to ever go through what I went through," Shapley said. "I love them too much."

Barlow maintains his innocence and Jeffs remains on the run.

Shapley said she does not believe capturing Jeffs will affect the proliferation of arranged underage marriages in the FLDS. She estimated the movement has 10,000 members and if Jeffs is caught, someone else will step in to carry out his work.

ABC's John Quinones reported this story for "Good Morning America."