It is not at all clear that the Mossad did this. Maybe this guy was standing in the way of something the US wanted, or Britain. It strains credulity to think that our intelligence service no longer kills their opposition. Personally, I think this sort of thing goes on all the time.
Just my two cents - from a casual observer. If what is said is true - that this guy arrived a lone and was without body guards, his assassins also had detailed knowledge of his advance movements, which to me indicates someone he trusted betrayed him. Also, I think if the Dubai police really had a clue, they wouldn’t be running to the media like they are.