He's going to need that good luck. Should have kept his mouth shut, seeing as how he didn't at least tell the parents about their boy's intentions. The only other way out (which he's closed off) is to claim he took the threats as typical idle/pissed chatter - no real intention, just blowing off steam.
I don't see Dalton in any legal trouble, he didn't assist or else he WOULD have kept his mouth shut, and there is no general (legal) duty to protect society from malcontents. But on a moral level, if he really thought the killer was serious, he can't just "let it pass."
Telling his parents? They are 21 year old men. Dalton should have gone to the cops if he thought he was serious.
But, really, how many 21 year olds out there talk sh!t and nothing comes of it.
Yup. He’ll get his 15 minutes of fame and pay dearly for every minute.