Try taking a look at the law and you will see why there was a decision not to prosecute.
Legal experts are in agreement here- no case would have any chance of meeting the required standards to prosecute an individual person. You would have to prove it was gross negligence, and in turn for which you would have to prove it was malicious, which you could never, ever do.
So instead the legal action is being taken against the Police as a whole for allowing a situation in which such a mistake could be made. It is hardly fair to blame the officers in the ground who were told a. it is a suicide bomber and b. take him out. They did their jobs 100%.
"The part that disturbs me the most is the part where they had him down on the floor and still decided to kill him. Made all the worse by the fact that they shot him seven times."
Those are the guidelines for dealing with suicide bombers. Any hesitation with the genuine article there and then you are dead, your colleagues are dead and a load of the public is dead.
The error is in the identification, NOT the methods. Those methods are essential if it ever is the real deal.