have had a role into it. they're looking into investigating what sort of role russia might have had. russia has a lot of chemical weapons experts. where they took off from, that's where russian personnel were at, and also, it was russia's responsibility, according to the u.n. mandate, to make sure and verify that all the chemical weapons under that 2013 deal were removed from the country. here are the details they're giving us. they have some pretty good pictures showing a big crater in the center of a street. they think this crater was caused by a chemical weapons-laden bomb and that they landed on 6:25 on tuesday morning. that's april 4th. they look at the rim of that crater and they see the telltale signs of staining, the kind of staining that would be caused by a chemical like sarin gas. here's what's interesting. after that, katy, they had some -- they saw a drone or some sort of unmanned vehicle taking