The idea that the mother could be an ... (spoiler)
The big reveal is that Agent Harker's mom is the accomplice. She delivers the dolls to those places, and the doll has the spirit of the Devil or something, which compels the father/husbands to kill the family and commit suicide.
My question is how could the mother avoid capture? Forensics wouldn't find traces of her DNA or fingerprints? Nobody in the neighborhood saw this woman in the area before or after the murders? We see scenes where the mother is covered in the blood, so she was right there. There should be traces of her that would be discoverable to CSU