MH & DK could have met online, DK might have presented himself as a different person, he seems to be in a fantasy world, a loner.
DK might have even been a 'look out' for someone else, could be too scared to say anything, could have had time to try and mastermind a blackmail attempt that went wrong, MH might not left his flat barefooted on a whim, as someone here said, not even thongs ? he might have left the flat in a rush,
Somehow this meek, quiet & seemingly weak ( in comparison to MH) just does not add up that overnight he turns into Jack The Ripper
DK could have phoned MH's advert, on some pretence that he was interested in having MH do a job for him, whilst simply planning a robbery.
I wrote previously that I don't believe MH was drugged, an overdose would have done the same job without a mess, perhaps there is evidence of this, glasses, drink - since no toxicology report has emerged, we are left to speculate
Lastly, I can't believe that MH would have been with this guy in any form, even if MH was experimenting or whatever else, I doubt he would have picked this naiive looking kid, whom he did not even know.