Police are given the authority to arrest and detain people.
They do not have the authority to become prosecutor, judge, jury, and executioner.
This is what the dispute is all about. Whether or not someone has an outstanding warrant, or a prior arrest record has nothing to do with it. Similarly, what the press says about it, or fails to say, has nothing to do with it.
This bears repeating and repeating until it's understood by all involved – including the Police Unions.