I have an issue with the question. As others have mentioned, police are people and with them comes all the faults in each of us. A better question might be, 'Do police act honorably?' We have every right to expect our cops to author accurate reports and testify about what they saw, heard and did.
I have never seen a cop decide to arrest a random person for no reason and clean it up later with lies. Where cops get in trouble is arresting someone who did do something illegal and either stretching the truth or making up lies to make it stick.