What can be done to keep cops from going rogue?

they need to get charged for murder if theyre going to do that

It comes from early settler days. Someone was elected Sheriff and he then appointed deputies, 'Good men and True' maybe but no job-education at all. And all too many Sheriffs offices still work like that. The biases and bigotry in the community pretty much becomes law. Like with the guy your link is about:

- Mexican name means Illegal immigrant means should be kicked out of the country, he will probably fire the moment we say "It is the Police, open the door" so we better do it first. This post was edited by JakobA the unAmerican. at July 26, 2017 6:00 PM MDT

Take their guns away. British cops don't carry them.