First off the guy was not guilty of anything we know of apart from not having a valid visa, no reason to kill him. If it was the streets would be littered with corpses.
As I said way back in this thread, the Judge ruled out "Unlawful Killing" as a verdict that the jury could return. An inquest is not a trial, back to civil law and "balance of probabilities" again.
For unlawful killing to be brought in it would have be clear that the officers who pulled the triggers did it independently. The question is did they BELIEVE that the guy was a threat to them and others based on the information they had at the time. Also bear in mind that their radios would probably not work on the station at that time so no contact with the surface.
What is clear is he didn't jump any barriers, run down the escalators or try to "get away", that is on CCTV. What happened on the train is from eye witnesses who were there at the time. Think if YOU saw a man being shot in the head right in front of you would you really remember what actually happened just before? Most of the people on the "tube" shut off and don't even look at anyone never mind pay attention to what's happening about them, first they would know was WTF was that bang.
The whole thing was a "screw up" through bad intelligence nothing more and nothing less, could it happen again? Yes it could, and it has happened before.
Sad case, lessons to be learnt no doubt, farce not IMHO.