A 14-year-old Howard County girl and her 19-year-old boyfriend were charged last month in the stabbing death of the girl’s father, Dennis Lane, a real estate executive and local blogger. Lane’s death in his Ellicott City home shocked the community, and police could offer no motive. While cases of children murdering parents are rare, Columbia-based psychologist Brad Sachs, who has extensive experience counseling families, talks about the dynamics of parents and troubled teens and the potential for violence in the most conflicted relationships.