I'm no expert in policing techniques, and of course it's only one account of what happened, but if this eyewitness report is true ...
Passenger Mark Whitby told Sky News he believed police had shot dead a man they had followed on to the train in "hot pursuit". He said officers held him down and "unloaded five shots into him ... he's dead". (Guardian Unlimited)
... they pushed him to the floor, bundled on top of him and unloaded five shots into him. (BBC)
... you've got to wonder whether dispatching five rounds into a suspect when you're already sitting on top of him is going to help or hinder a police investigation. Just a thought.