You have to know who is kidnapping you first though. I don't think most people would be able to figure it out in time when a bunch of camouflaged federal police jump out of an unmarked van. You've got maybe a second at best to make the decision, and if you've done nothing wrong the idea some unmarked federal police force you've never seen before is going to snatch you up is probably not even in the realm of your imagination, thus it must be criminal kidnappers.

Once again for clarity: you just don't know they are police.