So, he got over on his family because he is "a pretty good liar"

Minnesota Teen Planned to ‘Destroy Everyone’ in School Attack    By ABC News  Jun 25, 2014 8:26pm

A Minnesota teenager planned to “destroy everyone” in a massive attack on his high school and family, according to newly-released police interrogation tapes.
In the tapes, John David LaDue calmly outlined a plot to attack Waseca Junior and Senior High School, where he was an 11th grader. He said he’d “enter [the high school] and throw Molotov cocktails and pipe bombs and destroy everyone. And when the SWAT comes, I would destroy myself.”     “I was planning to dispose of my family, too,” he told police. “They did nothing wrong. I just wanted as many victims as possible.”

The alleged plot was revealed by authorities in early May after LaDue’s arrest the month before.
LaDue, 17, allegedly told authorities that he’d hidden his violent fantasies from everyone, including his father, according to the tapes.
“He thinks I’m just a good kid because I can lie pretty well and persuade him that I’m just ordinary,” he told police.                               READ MORE