Do you mean perjury as in its strictest definition of intentionally lying in a courtroom or under oath and the lie affects the outcome of a legal proceeding? Or are you including other lies or deceptive practices by law enforcers?
In any case:
1 - Signal: I seem to remember lower ranked law officers being forced by higher ups to lie in court to protect privileged wrongdoers.
2 - Stranger: In early episodes, law enforcement withhold evidence that would exonerate a suspect and commit perjury in the courtroom.
Bonus: Park Soo-ha's mindreading ability in I Hear Your Voice has him seeing through a lot of lies in the courtroom, but I don't think there's any actual perjury that he catches.
