And they offenders were arrested, tried and punished. The difference here is the police are never subject to the same justice.
https://www.google.com/amp/s/www.newyorker.com/news/news-des...
Normally, a union is formed to balance the power of capitalists with the laborers they employ. In the case of law enforcement, there is no capital, nor is their labor being used to produce something of value. If anything, law enforcement defends the interests of capitalists, rather than being subject to abuse by capitalists.