Here is an interesting article about why police officers lie under oath. It talks about quotas and how officers tend to lie in order to boast their reputation.

I have handled many criminal defense cases through the years, and have seen officers lie on the witness stand. I’m not saying all police officers lie. I know and have met many officers who are very professional and deadly honest. At the same time, I have met the few who are worse than the people they are arresting. It’s unfortunate that it only takes those few to make a whole department seem corrupt.