Well, speaking as someone who lived in a small town where the police softball team was one of the friendlier ones in the local league, you just have to use your judgment and/or your access to the holy spirit.

Some police are fine people; others are prejudiced or corrupt; others are mostly ok but occasionally get bent by pressure from above.

The precaution about not talking if you think you may be considered a suspect is just one of those necessary formalities, like putting important contracts into writing even when you trust the people involved.