The commissioner also raised the possibility that more potential suspects could be killed in the mass transit system, as armed officers are forced to make split-second decisions on whether a suspicious person who does not heed police warnings represents an immediate lethal threat and should be shot in the head.
"It wasn't just a random event, and the most important thing to recognize is that it is still happening out there," Sir Ian said Sunday in an interview with Sky News TV. He added, "Somebody else could be shot."
Adding to the anxiety in the country, he said that the four suspects who fled after attempted bombings last Thursday in London, which came two weeks after the July 7 attacks, were probably still somewhere in Britain.
Portraying the working environment of his police officers as "terrifying," he said that "there is no point shooting at somebody's chest, because that is where the bomb is likely to be."