Well, I think it's awesome that an arrest has been made! I'm impressed that all the mis-information we were fed was all for a good cause in the end.
I also think it's going to be quite a while (if ever) before we know the real reason behind this.
But taking into account some of the newer facts that have come to light, and the main one being that it was a 20yo guy behind it, I think we might all agree that it most likely was one of the following four scenarios:
1 - gay rendezvous gone wrong... not inconceivable since many closet gay/bi guys surround themselves with girls and outwardly appear to be extremely successful with girls. Often, gay guys seem to draw the girls... The grindr theory is interesting.
2 - drug deal gone wrong. This one works for me. Perhaps his regular guy didn't come through with the goods, so a friend has referred someone else to him whom he didn't know. It would explain the turning up to the pub in a bad mood, and then the pacing outside the pub after he's had to leave at closing time.
3 - boyfriend/brother/guy associated with some girl, who may have made a claim of rape or violence...
4 - random attack. Perhaps walked in on someone robbing the place, someone from the party at his apartment. Or maybe a combination of 2 or more of the above options. Like he tried hitting on a girl outside the party and someone else got jealous. Or perhaps after regular drug dealer didn't show and he tried his luck with a random at the neighbour's party.
Are there any other possibilities I may have missed?