Teen Charged With Parents’ Double Homicide On Primetime Crime

Tonight on Primetime Crime, they will be recalling the grisly murders of an Idaho couple, Alan and Diane Johnson who were shot to death in their home in September 2003.

In late June, judges in the Idaho Supreme Court upheld a jury verdict that Sarah, the Johnson's daughter, had brutally murdered her parents in 2003, a case solved by DNA and the then-16-year-old's suspicious behavior shortly after the bodies were found.

Sarah's motive — her parents tried to prevent her from seeing an older man.  Now Sarah Johnson has one last chance to convince a judge of her innocence.

For investigators, the first clues in the shocking case came when they discovered that Sarah had fallen in love with a Mexican man, who was in the country illegally. Alan and Diane did not approve of their daughter's relationship with Bruno Santos, a 19-year-old high school dropout from a poor home across town.

Relatives and friends stated that the Johnson family were arguing a lot and that Santos became the source of many heated family arguments.  Tensions mounted the Saturday of that Labor Day weekend, when Diane and Alan discovered that Sarah was sleeping over at Santos' apartment. When Alan picked up Sarah, he told Santos that he was to stay away from his daughter. He even threatened to report him to the police for having sex with an underage girl.

But Alan Johnson didn't get a chance to go to the police, he and his wife were dead that following Tuesday morning.

As investigators removed Alan and Diane's bodies from the house, they  noticed a coldness and distance from Sarah.  Just the beginning of her suspicious behavior.

I remember when this case happened, how horrified I was that a teenager, much less the daughter, could be capable of killing her own parents…and I'm still horrified.

You can read more about the Sarah Johnson case at ABCNews.com and tune in tonight on Primetime Crime on ABC at 10:00 p.m EST to see if Sarah can convince a judge she is innocent.