Transcript for The U.S and the U.N. Probe Syria
We turn overseas to syria and the stunning numbers tonight we heard from the state department, potentially more than 1,000 victims in the latest possible chemical attacks, the world still studying those disturbing images, the victims, women and children of this attack. This evening that disturbing headline from washington about what we could be looking at now. Unespecially inspector are facing huge hurdles to determine if chemicals weapons were, in fact, used. Reporter: It's a terrible and urgent task. Tonight the u.S. And un racing to find out whether chemical weapons killed these men, women and children. Just how many died? Today a shocking new number from opposition groups revealed in issue washington. The most recent sometimes we've seen range from 1,000 to 1800 which is a broad range. Reporter: The assad regime says the claims that it carried out a chemical attack are baseless. As un investigators beg for access to the site, the evidence may be quickly dissipating. David, tonight president obama has directed the intelligence community to do everything possible to find additional information about this suspected attack, but we don't know what the u.S. Response would be. David? Martha raddatz with us again tonight. Thank you. Also new word this evening on americans now believed to have joined the fight on the ground in syria potentially helping terrorist groups there. Could those americans, in fact, pose a threat to our homeland. Our senior justice correspondent sat down with robert muller today. We know muller is about to step down after 12 years. If your interview he was expressing concern about americans on the ground in syria? The fbi director is concerned about radicals who have gone to fight including members of al qaeda and he said there is intelligence americans may have joined them. You are concerned about what they number one the associations they will make and secondly the expertise they will develop and whether or not they will utilize that expertise to undertake an attack in the homeland. You asked what still keeps him up at night and what did he tell you. Reporter: He was blunt as always. He worries about terrorists taking on a plane with a bomb or using biological or chemical weapons. He said those threats are very, very real.
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