Believe it or not, the cops were legally ok to just watch! 5 times in the last 100 years the Supreme Court of the United States of America has ruled ( making it the law of the land ) that the police and other law enforcement officers have NO DUTY TO PROTECT ANY ONE!!!
they have a duty to investigate any crime with the intent and duty to assist the in prosecution of said crime. they work for the DA, attorney General of the state, or the federal attorneys and US attorney General in assisting in the prosecution of that crime.
the Justices have repeatedly said " if you get protection be thankful but its not their duty!
so legally as long as they were collecting evidence after and during the brawl.. they are free and clear!
