To run from armed police who are shouting at you (rather than shooting at you) at any time is an extremely bad idea… to do so at a time like this in London is utter madness.
Anyone running from armed cops who have challenged them first in London today should expect to get shot dead given the clear and present danger we are in… but that does not makes this any less of a horror. If Jean Charles de Menezes just reacted idiotically to the situation he found himself in, that does not mean we should feel distain for him.
We really need to know exactly what happened and why, but shooting a man dead who is suspected of being a suicide bomber and who is running away and trying to board a train(!) when being called on to stop is not the incorrect response. It was a tragedy of execution (in ever sense of the word) but not an incorrect policy.