Mr. Monk Goes to the Carnival - S1-E5
Plot hole: It makes no sense why the police haven't done the most obvious thing and checked for fingerprints on the murder weapon (the knife). It would not only back up the detective's claim that he did not stab the victim (he never touched the knife) but would have given the police a major clue to finding and prosecuting the murderer.
Answer: Stottlemeyer was already upset after the phone call. He was trying to get "Kevin" (who would have to be a judge, but no further character information is given) to issue a restraining order with no evidence of needing one, except that Adrian Monk said she needs one. Kevin said he would need to "sleep on it." So it's clear they've been trying to provide protection and unable to get the results they need, which seems to be based on no one trusting Monk the way Stottlemeyer does. He's just angry that they failed to protect Linda despite all their work. Although it does feel like a scene was cut, or altered, from the show that shows the futile attempts to protect Linda which built up to his outrage.
Bishop73