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Michelle Tessier, Deseret News
A police vehicle sits outside of a home Sunday, Sept. 28, 2014, where five members of the Strack family were found dead in Springville on Saturday, Sept. 27, 2014.

UTAH STATE PRISON — Dan Lafferty, who is serving a life prison sentence for a double murder he believes was directed by God says his ideas likely influenced a Springville couple's decision to fatally overdose along with their children.

Lafferty told the Associated Press on Thursday that he sees himself as the prophet Elijah and the world as hell, a philosophy that played into the September deaths of Benjamin and Kristi Strack.

Lafferty's 1984 killings of his sister-in-law, Brenda Lafferty, and her 15-month old daughter were chronicled in the 2003 Jon Krakauer book "Under the Banner of Heaven."

The 66-year-old Lafferty says he first became close to the couple about 10 years ago, after Kristi Strack had a dream about him while she was reading the book. She reached out to him, and eventually Kristi and Benjamin Strack became almost weekly visitors to the Utah State Prison.

Lafferty says he and Kristi Strack fell in love, something her husband was aware of and didn't mind. At one point, Lafferty cut off his waist-length hair and beard at her request and sent them to the family.

The friendship tapered off after the couple pleaded guilty to criminal charges including forgery and drug possession in 2008, which ended their prison visiting privileges.

They exchanged letters afterward, but Lafferty said Kristi Strack didn't believe he was Elijah, and when he persisted she quit answering his letters.

Lafferty says he hadn't talked to the couple for years and didn't know of their plans or mindset.

"I'll miss them, but I'm happy for them," he said. "I believe they're in paradise now."

Lafferty, who is polite and friendly in conversation, has a self-devised philosophy that he refers to as his insanity; though he says he's not crazy.

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