responsibility by isis, by al qaeda, that the acting deputy commissioner -- >> this was potentially a lone lunatic, a maniac. a british newspaper is describing this. taken it upon himself to do this, strike horror in the heart of british democracy. heard the prime minister theresa may describing it as sick and depraved. >> his face. it's an image that is so evocative about what this means, what this attack means. and as you so evocatively describe it, an attacker who uses a vehicle as far as i can tell from the pictures, then goes on to use a knife that must be a guess -- >> around 16 inches. >> so what you're left with is the sense that how do you stop this? we may be facing this for years. for decades. because while you can protect places like this, you cannot protect against someone being inspired to do something like this on their own. >> the brits don't like the kind of huge hulking visible security that we've come to accept in this country. and by that i mean look at our presidential motorcades. the enormous black suvs. the shot we saw of the silver jaguar going down the street was theresa m