A TEENAGE DAUGHTER'S ALLEGED GRISLY PLOT TO MURDER HER MOTHER IS CAUGHT ON TAPE, ON ABC NEWS' "20/20," FRIDAY, JUNE 6

Plus: A Dark Secret Turns Deadly When a Loving Father Murders His Twin Daughters � Who's to Blame?

And: Brian Ross' Investigation Into Doomsday Religious Sect

Also: Running on Empty � How Much Gas Is Really in the Tank?

Colleen Stribel was in for the shock of her life when the Watertown, TN sheriff's office broke the surreal news to her that her own 19-year-old daughter, Lauren, was plotting to kill her. The alleged motive: conflicts with her mother and a two-million-dollar life insurance policy, for which Lauren was the sole beneficiary. Lauren, along with her boyfriend and another boy, was caught on police audio tape mapping out the gruesome details of the alleged murder plot. "If you hit her with a shotgun, don't hit her in the face, please," Lauren was heard saying. She's now charged with conspiracy to commit murder. The report airs on "20/20," FRIDAY, JUNE 6 (10:00-11:00 p.m., ET) on ABC.

How did a typical mother-daughter relationship turn to talk of murder? "I will tell you that I was in total shock� no one writes the handbook on that one," Colleen tells JuJu Chang. With her lawyer on hand, Lauren says she was just talking and never would have gone through with the alleged plot. "Absolutely not. I can barely even, you know, stand to see a mouse caught in a mousetrap," she says.

Then: The Crespi family of North Carolina appeared to have it all � loving parents, a beautiful home and five healthy children. But they also harbored a dark secret about their father, David, that threatened to destroy it all � and it did. Crippling bouts of depression led David to suicidal thoughts. Yet he promised his wife Kim that he would not take his life. Instead, he did the unthinkable. David murdered his five-year-old twin daughters, stabbing each multiple times. Only when tragedy caused their world to crumble did the family discover the truth about David's mental health and learn the power of forgiveness. Kim continues to stand by David's side and blames the psychiatrists and therapists who, she says, missed a critical diagnosis. For the first time David talks to a reporter face-to-face. Jim Avila reports.

Also: Is the House of Yahweh a "sex cult" run by a bigamist, as some former members claim? In an in-depth investigation, ABC News Chief Investigative Correspondent Brian Ross reports on the Texas religious group and its 73-year-old controversial pastor, Yisrayl Bill Hawkins, who just last month was charged with encouraging bigamy.

In an interview for "20/20," Hawkins' former wife, Kay, says he began to preach polygamy after he was caught having an affair with a church secretary. "He began to rewrite the Scriptures," she said. "Any Scripture that did not go along with more than one wife was rewritten to imply that it was all right to have more than one wife."

Hawkins told "20/20" he has only "one wife" and that he is being persecuted because of his religious beliefs. "They hated me more than anybody that's ever been arrested in Callahan County," he stated. "There's nothing wrong, according to the Yahweh's laws," with having more than one wife, Hawkins said. But he insisted he follows the "laws of man," which prohibit multiple wives. Hawkins also tells "20/20" about his doomsday prediction of a nuclear war he claims will begin on June 12.

Plus: Even when your car's gas gauge reads "empty," there is still more gas left in the tank. Is that a myth or does empty mean empty? John Stossel reports. (OAD: 12/2007)

"20/20" is anchored by Elizabeth Vargas and John Stossel. David Sloan is executive producer.