The problem with all these thoughts is that no-one that isn't at an incident will really know what happened.
The story certainly being told is that they guy was challenged from behind and didn't have a clue what was going on.
Now if this is the real story (and not having been there I don't know for sure)
then if it was me walking along the street minding my own business (and had he not been to the pub?) and somebody from out the blue shouted armed police stand still or whatever, I would turn round to see what was going on, automatic reaction especially if you aren't aware or expecting it to have anything to do with you.
Now if the story is true (and remember I have only what has been put on telly) that they had the guy covered from behind then hard questions need to be asked about how the guy got shot in the head, not in the chest. The guy was just walking down the street minding his own business