Somehow, DM made arrangements to meet someone at the hotel.
If LE can't or hasn't found evidence of these communications, then he must have had another phone, a "secret" phone, Imo. And the perp took it. If this is the case, I can't imagine how they will trace this person, if they really do not know who it is. I just don't believe this was all arranged verbally.
But I still think he was lured there to be killed, by someone who was acting on behalf of another person. The person requested that his death be made to look like something else, i.e not a straight robbery, suicide or accident and did not mind if DM was humiliated. Who benefits from his death in any way? Or hated him enough to have him murdered? I don't think it was about money owed. DM would have had to double-cross someone, or cause them great harm in some way. A jilted mistress isn't working for me, though.
Jmo