the plea agreement doesn't necesarrily mean he's guilty. it could have been a situation where an innocent plea would have been more costly.
i don't know whether the father and son are guilty or not, but i do know that one of the most dangerous things to the civil liberties of americans is to assume that the police BY DEFINITION cannot be wrong.
Then by all means, do not do so. But you also shouldn't assume that a person who pleads guilty is actually innocent.