by the bbc'sd security correspondent as well as rick pereira who served at the national counter -- counter- terrorism center. gordon, let me talk to you. evidence would leave them to who is behind this. is that where people will start? >> that is right. they will try to determine what kind of the the device was used, how it was detonated. that will lead them to closed- circuit surveillance, which is likely to be a lot given the area. it might help identify whoever plays these items in the area. follow theill evidence trail. not know who is behind this. police are not saying. we cannot say whether this is either domestic or international. what are the things that you are piecing together out of what happened in boston? what will forensics people and investigators look at? >> kollhoff can be told by the sophistication of the device -- >> i lot can be told by the sophistication of the device and the coordination of the device. >> what was the size? >> based on the explosions, relatively small, but it still had a gift -- a detrimental effect on the people nearby. is isoup or whoever this able

by the bbc'sd security correspondent as well as rick pereira who served at the national counter -- counter- terrorism center. gordon, let me talk to you. evidence would leave them to who is behind this. is that where people will start? >> that is right. they will try to determine what kind of the the device was used, how it was detonated. that will lead them to closed- circuit surveillance, which is likely to be a lot given the area. it might help identify whoever plays these items in the area. follow theill evidence trail. not know who is behind this. police are not saying. we cannot say whether this is either domestic or international. what are the things that you are piecing together out of what happened in boston? what will forensics people and investigators look at? >> kollhoff can be told by the sophistication of the device -- >> i lot can be told by the sophistication of the device and the coordination of the device. >> what was the size? >> based on the explosions, relatively small, but it still had a gift -- a detrimental effect on the people nearby. is isoup or whoever this able