Feds Chase Leads in Boston Marathon Bombing

Law enforcement analyzing clues, but no suspects held.
2:18 | 04/16/13

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Transcript for Feds Chase Leads in Boston Marathon Bombing
Of course investigators have been frantically searching. Overnight for any clues as to who might be responsible for this and ABC's chief investigative correspondent Brian Ross who's covered terrorism for so many years of attractiveness. All day all night Brian what can you tell us we'll just -- nobody in custody and no sense that there could be more attacks coming in the search for the killers. -- behind this attack could not be more urgent with hundreds of police and federal agents assigned to attacks. Overnight a tip about possible explosives led federal agents to search -- apartment on the fifth floor of this building in the Boston suburb of Revere. Agents later told residents there was nothing to worry about. But the quick law enforcement response underscored the urgency of the FBI's effort to track and stop the people responsible for Monday's attack. I encourage everyone to -- heightened state of vigilance here in the Boston area. BI agents also -- to a local hospital to question a twenty year old Saudi college student who was injured in the blast went. Authorities stressed he is not considered a suspect. There are people who we are talking to but there is -- suspect is for him home in moments hospital. So far those videos of the blast everybody in -- the most important news. Authorities say the white smoke seen after the detonation. -- small -- with a simple low velocity explosive mixture not military grade but still sophisticated enough to detonate about fifteen seconds apart. At. -- had to be forces as we've seen in other bomb attacks but they knew how to make the -- on global. Experts say the large pieces of metal as seen here in the it just the bomb -- had been concealed in the mailbox or trashed her as one witness described. I literally saw the guard brings -- I saw this last -- smoke and -- -- friends Jessica. And the limited damage to nearby buildings tells experts but the bomb may have failed to fully function as designed. In other -- as bad as it was it could have been worse him. At this point authorities say they still don't know enough to rule in -- rule allowed domestic or international terrorist charge. O'Brien thanks very much.

This transcript has been automatically generated and may not be 100% accurate.

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