Kristi Strack and Dan Lafferty struck up an unusual relationship behind prison walls a decade ago.

She dreamed about the prisoner who murdered a family member and an infant in what he called the name of God in 1984. She wrote him letters and began visiting him in prison. He said they fell in love. At one point he cut off his beard and waist-length ponytail that had been growing for about 15 years and mailed it to her. In recent years, they drifted apart as she questioned his status as a prophet and Strack was banned from visiting the prison.

Strack killed herself by overdosing on a concoction of methadone and cold medicine with her husband, Benjamin, and three children in September, and authorities wrapped up the investigation this week.

In a Thursday interview with The Associated Press from behind Plexiglas at the Utah State Prison, Lafferty said his hell-on-earth philosophy that says the world is controlled by the devil likely influenced their suicides. Investigators cited the couple's belief in apocalyptic ideology as a reason why they carried out the killings.

"My 'insanity' messes with people's lives," Lafferty said. "It's just the way it is."

The Strack family has said that mental illness was a factor in their relatives' deaths, and that better screening could have prevented the tragedy.

Lafferty sees himself as the prophet Elijah with responsibility to prepare the world for the second coming. He has few followers, but he says the Stracks were, at least for a time, believers.

The relationship began with her reading the 2003 Jon Krakauer book "Under the Banner of Heaven" that chronicled Lafferty's slayings of his sister-in-law, Brenda Lafferty, and her 15-month old daughter.

The couple started visiting almost weekly, Lafferty said, and spent hours on other days talking on the phone. Lafferty says he fell in love with her. Some of those conversations were sexual, and Kristi once shared a photo of herself in her pajamas, he said.

At 66, Lafferty is polite and friendly. Slightly built and wearing tortoise shell glasses, his hair was neatly combed with a small beard.

In his philosophy the world is controlled by the devil and the apocalypse is near. He refers to it all as his insanity; though he says he's not crazy.

Kristi Stack and Lafferty hadn't been in touch for years, he said.

The relationship tapered off after the couple pleaded guilty to criminal charges including forgery and drug possession in 2008, which ended their prison visiting privileges. They continued to exchange letters, he said, but Strack doubted Lafferty was Elijah. When he persisted, the letters stopped.

"I believe they're in paradise now," he said of the Stracks.

Rick Ross, executive director of The Cult Education Institute, said Lafferty is a cult leader with a small following who can nevertheless wield a dangerous influence, even from behind prison walls.

"With Lafferty and those that pose as prophets, they all created a kind of doomsday, crisis mentality where people felt there was nothing in the world left to live for," said Ross. "When they killed themselves, they felt like they were doing something that was good."

Lafferty is serving a life sentence and his brother, Ron Lafferty, is on death row after being convicted in the slaying of Brenda Lafferty after she resisted her husband's entry into a radical group that espoused polygamy and other early Mormon ideas.

There was an apocalyptic strain to the early Mormon church, historian Ken Driggs said.

"They were very millennial, they thought the second coming was imminent," he said.

The Stracks talked often about their fear of an impending apocalypse, police said.

Lt. David Caron said Thursday that Lafferty initially denied influencing the Stracks, and said the relationship was more fatherly. Police interviewed Lafferty during their investigation, and found that he'd had no recent contact with the couple and was unaware of any suicide plans.