– Why has this automatically been pegged as murder? Isn't that risky in terms of a trial?
It isn't automatic. The police base charges on the forensic and circumstantial evidence.
For it to be murder, wouldn't they have to have proof he lured her into his room with the explicit intent of murdering her?
No.
That seems insanely, insanely cold. The bloke seemed weird and off-kilter but that sort of planning is something else. Why are they so confident it went this way, as opposed to something that'd result in manslaughter?
The circumstances in which a healthy 22 year old female dies by accident in your hotel room on a Saturday night are pretty limited.
Drug overdose?
Any form of substantial physical attack on the victim will fall within the definition of murder.