That’s the problem. Not calling the cops doesn’t solve the problem. It turns it into a civil matter rather than the criminal act it is. By not calling the authorities and pressing charges, they just gave tacit approval to the behavior. It wasn’t like this assault was some he-said, she-said — it was indisputable with witnesses.
Call the cops. Get these guys sent to prison. That does a lot more than blogging vigorously about one’s displeasure.