Of course the police were culpable, of course they lied, of course they backed each other up in those lies. They are policemen aren't they?
Policemen on the whole, suffer from an over inflated sense of their own importance, they get respect and privileges based on the uniform they wear, rather than on the person wearing it.
It makes them think they are different, and special. It takes a person with a lot of personal integrity to survive this unreal situation, and be a 'good copper' They are around, but there is not enough of them.