Here's why people trust Watts over the cops involved: because there are witnesses, because Watts has provided a lot of detail, and because the only official police statements have included at least one big mistake, claiming he was trying to go from Canada into the USA instead of the opposite.
Really? All I see are a bunch of sycophants crying and clamoring in order to get free publicity for some obscure sci-fi writer most people haven't even heard of. They're also parading around his 'celebrity' status as a writer because, somehow, that's relevant to anything at all. Oh wait, no it's not.
Watts and his supporters wouldn't be hoping the situation was videotaped by security cameras if he was the one misrepresenting the situation.
Yeah, because knowing there isn't any videotape of the situation sure makes it easier to spin the encounter their way. And hey, they're "hoping" that it was filmed (even though they know it wasn't), so clearly they're in the right! And whoever-this-random-guy-is really is a saint of saints and did nothing to provoke the situation.
Damn those black-hearted law enforcement officers! Ooh, they're so evil! Burn them! BURN THEM ALL! AMG!!!

