does this look like the mark of isis or is there any way to know that? >> ta pt is certainly the go-to explosive for isis right now because you can make it at home with peroxide and as he tone which you can get in stores. but they're going to claim it no matter what. and i don't believe it was anything more than an isis inspired attack, if that. it was somebody who was not in contact with them, who took this upon themselves to do it for whatever reason he felt he needed to contribute to jihad. >> and as far as trying to thwart these type attacks, steve, london has been hit over and over again and now it's the subway, the tube, the oldest subway in the world. it's very, very difficult to thwart something like this just as somebody behind the wheel of a car that runs people over.