Thirty years ago, Dan Lafferty and his brother grew their hair long, called themselves prophets and claimed God told them to kill their sister-in-law and her baby after she resisted her husband's entry into a radical polygamous group.

Kristi Strack was 6 years old when it happened, but police said she developed an obsession with the case that turned into a close yearslong friendship with the imprisoned man.

The mindset of Strack and her husband, Benjamin, grew increasingly bizarre, culminating with a belief that the apocalypse was near just before they killed themselves with a drug overdose and took their three children with them.

Police still aren't sure exactly what led them to commit suicide in September.

The July 1984 slayings of Brenda Lafferty and her baby daughter were chronicled in Jon Krakauer's 2003 book "Under the Banner of Heaven."

Kristi Strack eventually reached out to Dan Lafferty's daughter, said Springville police Cpl. Greg Turnbow. Strack and her husband became close friends with him for several years.

"He's very fond of them," Turnbow said. "He wanted his remains to go to them."

Dan Lafferty communicated with Kristi Strack like she was one of his children, police said. When she suffered a bout with ovarian cancer, there was talk about Lafferty being able to cure it, police said.

Turnbow said he talked to Lafferty as part of his investigation of the Stracks' deaths, and the inmate said he believed himself to be the biblical prophet Elijah. His role would be to announce the second coming of Christ, the Deseret News has reported, but police said he didn't generally talk about the end of the world with the Stracks.

The Stracks' close, frequent communication with Lafferty didn't raise any concerns by Utah prison officials, and there generally isn't any reason it would, said spokeswoman Brooke Adams. That changed in 2008, after Kristi Strack tried to pass her brother off as her husband so he could come on a prison visit and authorities revoked her visiting privileges, Turnbow said.

Lafferty's contact with the couple ended.

The same year, Benjamin and Kristi Strack began homeschooling their children. Court records show the couple pleaded guilty to misdemeanor forgery charges in 2008 and disorderly conduct in 2009, part of a minor criminal history that spanned about 12 years.

The couple also had gone through court-ordered drug treatment, but Elizabeth Sollis, a spokeswoman for Utah child welfare services, said Wednesday that's not necessarily a reason for state workers to intervene in a family. Police said there was no such intervention in the Stracks' case.

Kristi Strack, 36, was being prescribed methadone for opiate addiction at the time of her death, and that's how investigators believe she got the methadone used in the overdose deaths.

The children — Benson, 14, Emery, 12, and Zion, 11 — were sheltered, Turnbow said. There's no evidence the family attended any churches, and when some members of The Church of Jesus Christ of Latter-day Saints reached out to them, they would politely refuse, Turnbow said.

Police didn't find any writings to show exactly what Benjamin and Kristi Strack believed when they died, but they often talked with family and friends about wanting to escape what they saw as a growing evil in the world. Friends and family thought that meant they would one day move somewhere remote and live "off the grid," but no one thought they'd kill themselves, police said.

Benjamin Strack, 37, hadn't been to work for a week when Kristi Strack's older son from a previous marriage found the family's bodies in a locked bedroom Sept. 27. Police found traces of a lethal drug mixture in a child's sand pail in the room.

After the deaths, police found a letter from Benson Strack to his best friend bequeathing some of his possessions, showing that the teen thought he might be found dead one day.

It's not clear how much the other children knew about the lethal mixture of drugs they ingested, police said. The combination of methadone and cold medicine found in their bodies would likely have made them very sleepy just before they died. There were no signs of trauma or a struggle.

The younger children's deaths were ruled homicides since they were too young to consent to any kind of suicide plan.