Get outta' here with wanting documentation. "They say" is all you need. [Coffee]
My take on why it wouldn't ge good for Antifa to head out of the city? Big city PDs run by liberals are way more likely to let the shenanigans continue as opposed to a Sheriff in a red county. Send enough perpetrators out in body bags, it sends a message. For example, gangs in LA used to rob banks in Bakersfield. Guess why they don't do that anymore?