with a murderer. >> reporter: but, to protect the investigation sergeant slot gives no details to kent whitakert show their whole deck of cards, but they could at least tell me something if they wanted me to believe them. >> kent's response to me was, "you guys are either way wrong, or my son's a monster." >> reporter: despite the warning, kent lets bart move back home and for the next several months bart spends every free moment with his father, playing the perfect son, studying the bible. >> he appeared as if he was really listening. and i told him, "bart, i can't read your heart. you're either zero percent responsible or a hundred percent responsible. the point is that i love you. god has allowed me to forgive everyone involved." >> he truly forgave the person that did this. i mean, he was the first real christian that i'd ever met that really did what jesus christ told him to do. >> reporter: he asked you point blank, "did you do it, bart?" >> yeah. >> reporter: and you said, "no, dad." >> yeah, i did. >> reporter: even though he was going to forgive you. >> yeah, but it's not that simple.