Police are the violence enacted by the state to protect capitalist interests.
While they incidentally help in sometimes solving crime, this is not and never was, their true purpose.
Making sure the proletariat do not gain class consciousness and making sure power can not shift from capital is their job.
When people say ACAB it means that because they are tools of the capitalist elite they cannot definitionally be anything other than bastards who are ignorant of class consciousness or are willing participants in their own abuse at the hands of capitalists using them because it gives them some kind of proxy power.