[BostonGuy]

Dry run for the real thing, to be performed later, maybe?

Possible, but unlikely. If the terrorists got their hands on a crop duster and the necessary bio agents, why risk capture with a dry run?

[umbra]

Or why spray a coal barge in the middle of nowhere? Did they think no one would notice a maniac crop duster spraying boats with chemicals in the middle of the Missippi River?