-- -- -- -- drives us Pierre Thomas in Washington Chief Justice correspondent -- let me begin -- you. Intelligence officials trying to -- -- rolling in her ruling out anything at this point and one of... See More
-- -- -- -- drives us Pierre Thomas in Washington Chief Justice correspondent -- let me begin -- you. Intelligence officials trying to -- -- rolling in her ruling out anything at this point and one of the things that's so mystifying no one is supported -- responsibility. Plus spoke to a senior official this morning -- said typically. In the hours after a bombing like this terror organizations like the claimed responsibility. Want the credit for their daily work. A number of people were interviewed overnight -- I can tell you some associated with that Saudi student -- in the hospital. My sources -- besides they still don't know of these young -- had anything to do with the bombing bombing. But out of an abundance of caution they're trying to dissect his life. -- piecing together the bomb -- Because the FBI the bureau of alcohol -- -- farms have a vast catalog of past bombing incidents didn't compare that. Whatever information they can get about these particular devices and try to come up with a list of potential suspect. And -- this is exactly the kind of attack Homeland Security officials are worried about for the last. Several years not necessarily all that sophisticated but attacking soft. Exactly -- -- reasonably confident that they could prevent -- nine elevenths scale attack something few. Which could involve a lot of people -- what they worried about were small scale attacks like this which would probably involve a small number of people. That would go after a soft target. Large numbers of people killed where security while barely exists could -- Okay good thanks very much in Martha Raddatz here one of the -- Elements of this whole bombing here is. Relatively crude bombs bombs in the kinds of injuries you saw in Iraq and Afghan. Afghanistan is on the mall in time this this whole street this whole scene is so reminiscent. Of -- -- is in Baghdad in Afghanistan. When the war in Iraq began. There were very small bombs they were not military grade bonds that they do a great deal of damage and those kinds of bombs would be placed in backpacks they would be placed on the side of the road. Precisely that target people walking by and and we're learning on the here's that so many of the victims. Are exactly the kind that a lot of our service that people who died in Iraq and Afghanistan this is going to be a it's going to be a very long recovery and and you have to think about it those people had no protection. In Iraq and Afghanistan at least they had body armor at least they were ready to fight back. Here you've got all these innocent victims on the street. And their shorts and their flip flops just enjoying the day it's going to be a long long recovery for these people didn't want to thanks them.
This transcript has been automatically generated and may not be 100% accurate.