MOST cops are dirty.
One easy way to tell is to look at statisically significant surveys of corruption. For example, 80% of CHP chiefs retire in disability.
That means that, even compared with the typically fraudulent and corrupt disability retirement rate for cops, CHP chiefs are Kings of Corruption. They are literaly bigger felons, in terms of ill gotten gains, than 99% of drug dealers.
Cops lie and defraud casually, because they think they are entitled, and because they think they will never be called to account. No matter what rock you turn over in law enforcement, you find corruption. The only difference between US and Mexico cops is that US cops find it easier to defraud the system and taxpayers as a class than to engage in retail corruption, though plenty of them do that, too.
And the whole Catholic Irish cop thing is passe: corruption among cops knows no race or sex boundary. Why do you ask?