I am rather skeptical of the * departed on foot* story at the moment - if AP offered her a lift, as he says, then why would she not take it - at 4am on a cold dark morning
Even if she refused the offer of a lift, what person would let a lady just walk out into the night, with no coat and high heels on?
Surely you'd phone a taxi and if she refused that due to the cost, you would pay for it for her, seeing as you were the reason she'd left her friends to come to your flat.
If she didn't trust taxi drivers for safety reasons, then you'd offer to go back with her (after all, she apparently trusted him enough to go to his flat a few hours earlier).
If she didn't want that, then wouldn't you suggest calling a friend to collected her?
And if she didn't want to disturb friends and was insisting on walking home, as a last resort you would walk her home.
If she refused all of the above, then either she clearly didn't want to spend another minute with him for whatever reason, or was ridiculously independent and naive with regards to the area ................ or events didn't happen like what we're being told, imo.
And if he didn't make all those suggestions, then he should take a look at his own behaviour, regardless of whether he is involved in her disappearance.