A quick update to my post below. The Guardian has an interesting, if brief, leader on the subject today, which illustrates nicely just how many questions remain to be asked about this shooting, and just how the evidence doesn't seem to add up. Firstly, it now seems that De Menezes, the victim, lived in a block of flats under surveillance - not a "house", as originally indicated. Also, he took the bus, accompanied by the policemen, to the tube station - yet they chose not to challenge him at this stage. Perhaps an odd decision, given that some of the recent bombings and attempted bombings have been on buses.
Certainly, we need to know more before condemning the officers involved; most importantly, to what extent they were acting on the evidence in front of them, and to what extent they had prior (if, apparently, deeply flawed) intelligence stating that De Menezes was a suicide bomber. The investigations (both internal and external) must deal with these questions fully and frankly - and not hesitate to put the matter to criminal trial if, as seems quite possible, the facts warrant such a course of action. In the meantime, we can but agree with another writer in the Guardian, who notes:
The dominant mood that we are better safe than sorry is understandable. But after Friday's incident we are left with one man dead, nobody safe and everybody sorry. If there's one thing we've learned over the past two years, it's that a pre-emptive strike with no evidence causes more problems than it solves.