The FBI's Investigation of Chip's Family

The day after the murders, Robert had carpets in his home steam cleaned. One of Chip's adult sons kept a collection of knives. The other son had once made a disturbing drawing of a man holding a knife over the bed of two people while they slept. If you put these factors together, it is obviously various suspicious things, behaviors, things that police have figured out about Chip's family. But that doesn't rise to the level of making them actual suspects.