dan colson and bomb expert rick hundred. rick, let me start with you, pressure cooker bombs. look at this. we have pellets, we have bbs, we have ball bearings, nails without their heads on them. tell us about this type of device. >> clearly, sean, this is a device that is designed to be as anti-personnel as possible. this is your landmine sort of thing that is built strictly to be doing as much damage to human beings as possible. the pressure cooker itself serves as a veeset to contain the pressure of the explosive. in this case we probably have a homemade explosive just based on the smoke you see and a low explosive maybe trying to kick it off. >> obviously they want to know what explosives were used, a, and maybe you have some thoughts as to what that might be. obviously. and certainly the component, how this was triggered. what are your thoughts? what are they looking for and what would it tell them? >> first of all, homemade explosives, for one thing that means they will be cooking them up somewhere. maybe in an apartment, maybe in -- >> what do you mean by cook them up?