I think #1 and #3 are related.
Like MassGuy, I agree there's a big piece of the puzzle missing, by design. I also wonder about the US Marshals inclusion in the investigation. Not being an American I usually relate US Marshal involvement as chasing down fugitives. Mostly from movies. So who's the fugitive?
I was also wondering about the XBox. I thought it was just for playing games but you can converse with others, in group chats, too. The only account that has been suggested as being Caleb's is the Reddit account. Not verified since I believe it was found by a civilian not LE. Could they have other information from Caleb's XBox that is driving the investigation?
If CH did meet someone for a hook up, what if he met up with someone who turned out to be a known quantity, someone from the university.