The group claiming responsibility for the attack tonight they're called -- Bob they are linked to al-Qaeda at a CB US authorities say they have recruited Americans before. ABC's chief investigative... See More
The group claiming responsibility for the attack tonight they're called -- Bob they are linked to al-Qaeda at a CB US authorities say they have recruited Americans before. ABC's chief investigative correspondent Brian Ross working that part of the story tonight in his what is right here right good -- Good evening David indeed no terror group has been more successful in recruiting Americans to its ranks and Tulsa Bob he even has has carried out a series of increasingly brutal attack. US officials estimate that as many as fifty Americans. Travel and training camps in Somalia and signed on as recruits to two over the last six years. It's extremely deadly organization very well trained and these were the only -- -- affiliates. Which actually has actively recruited here in the United States. Just last month Al -- posted this online recruiting video with three young -- it said -- from Minneapolis and later died as a martyr. You guys only know. Moments when we ever hear this parade. Can -- come here another American Omar how mommy and Daphne Alabama. Rose to a leadership position -- -- to -- until he was reportedly killed by rivals in the group earlier this month. One of the things that we believe we 64 in the Clinton ours is to die as martyr a mommy and other -- -- leaders have vowed to hit US targets. And officials worry the American recruits still there could return home -- that in mind this is. Something scary -- -- if you think about individuals who went and fought in. A place like Somalia when they come back home there's nothing good -- come out of this. What you see today in Kenya can be easily copied here in the United States. The FBI has brought criminal cases against some of the Americans who went to Somalia and came back to the US. But today the FBI -- the law enforcement officials say they have no indication. -- out -- -- and any plans or indeed even the capacity to attack here in the US and course Brian what we don't know is if any these recruits played any role this plot. That's right and we won't know probably -- the -- is over.
This transcript has been automatically generated and may not be 100% accurate.