And now, we go overseas to syria. The rebels still on the move, near the capital damascus. The assad regime, still core ra its weapons. And abc's alex marquardt got a call to travel at night and meet... See More
And now, we go overseas to syria. The rebels still on the move, near the capital damascus. The assad regime, still core ra its weapons. And abc's alex marquardt got a call to travel at night and meet with a defector, who knows about those weapons. A former general in ling regime. Reporter: The rebels have taken the fight to syria's biggest cities. Today, battling near assad's stronghold, his palace in damascus. While fighters have overrun one of the regime's largest military bases, outside the city of aleppo. American officials say they fear the likelihood of assad using chemical weapons is rising and say they have proof they've been prepared. We went to meet a man who shares those fears. Driving along a back country road near turkey's border with syria. His name is adnan sillou. He told us until 2008, he was a chief of staff in the chemical weapons program. He said he worked on the defense side, in charge of preparing troops for dealing with attacks and safety equipment. What specific chemical weapons does the assad regime have? He said, "they have mustard gas, along with the highly toxic nerve agents vx, sarin and that bun." The regime has started to fall and deteriorate, he argues. It's highly possible assad will start using chemical weapons to kill his own people. I think it's a last ditch effort and one that don't want to use are increasingly considering it. Reporter: If the regime crumbles, the u.S. Fears the weapons could be transferred to hezbollah, or fall into the hands of groups like al qaeda. Knowing what you do about the facilities, the security, do you worry that these weapons will fall into the wrong hands? "Yes," he said. "There's an extremely big concern they'll fall into other hands." Sillou says he was interviewed by the cia when he left syria. Now, he's pleading for the u.S. To give him money and weapons so that he can lead a brigade of fighters back into syria and secure those sites.
This transcript has been automatically generated and may not be 100% accurate.