This I thought was a good summary

"- He came out of a building where some of the occupants were under
surveillance.

- He was not a primary suspect (i.e., one of those directly watched)
but would still be a person of interest - not because of his colour,
nationality, religion or any other discriminatory reason but purely
because he was living in the same building as the primary suspect(s).

- As a "person of interest", there is no reason to stop him straight
away. He was followed and observed.

- The observer(s) called in when he was queueing for the bus to find
out what procedure to follow (stop him now or carry on following).

- The response did not come back from command quick enough to prevent
him boarding the bus. This is a command failure, not a failing of the
officer at the scene. As a result, the preceding orders still held:
observe but do not approach.

- The observer(s) boarded the bus with the suspect in order to
maintain this contact. If the observer was to avoid raising the
suspect's suspicions, he would not be seated very close by.

- During the bus journey, the suspect made a call on his mobile.

- Someone several seats away is unlikely to actually hear the
conversation (never mind discern between different accents)
but would report through the fact that the suspect has initiated
the call (i.e., more information for command).

- Unless this suspect had been followed previously (unlikely given
that the building had only just been linked to the recent bombings)
there would be no prior knowledge of the suspect's destination.

- When the suspect disembarked (location and direction information
again passed through to command) a further decision had to be made
whether to continue to observe or to stop him.

- When it became apparent that the tube station was his destination,
the critical decision of "what to do" was resolved: he had to be
stopped.

- The "shoot to kill" / "head shot" policy has been in place for
suspected suicide bombers for a long time so armed response officers
would be familiar with the procedure to adopt.

From command's view, they have a nondescript "other" (an unknown to
the ongoing security investigation) leaving a "building of interest",
being followed as a matter of course, making a phonecall then going
into a tube station. Normally this would not be a problem but when
it is the day after a synchronised set of bombs failed and a fortnight
after a synchronised set of bombed worked, the priorities associated
with each element change - the risk of "getting it wrong" is far more
severe than the risk of any upset from detaining an innocent guy.

When this innocent guy jumps the barrier and runs down an escalator
towards the platform, he is suddenly not considered "innocent" any
more.

In those last few seconds, the only choices were to gamble on the
guy turning out to still be innocent (assuming you can catch up with
him again) or to shoot to kill.

A month ago, he would have lived to regret his stupidity but, on that
day, there would be very few commanders who would not have made the
same decision."

Posted By: Winged Eel Creosote, Jul 26, 16:15:03