Unless the First Amendment has been repealed in your area, you are welcome to record and publish what you can lawfully observe. The cops would have loved to have been able to arrest and convict the person filming them illegally beating Rodney King, but because of Rodney King sorts of malefactions by the cops [which happen more than people, and The People, want to admit], you may and should record police interactions between them the the people the serve. Remember that the citizens are the masters and the cops are the servants in this land of popular sovereignty.