To do what they did means they had to have had access to knowledge and resources..

[ There's a slow nod in answer to his surmise. ]

Likely someone at ground zero, with or without an antidote so they could determine success, someone above and someone further out. I'd say... About there-- [she points to one of the roof tops, decked with banners to and fro] and... Somewhere half way. Relatively clear view...

That fountain.