Murdered a completely innocent dude in his own house? How is this a fucking question?
Think about it: it's kind like driving drunk and not getting a DUI. Instead of impaired driver behind a dangerous vehicle, we have a tired, armed, cop. Same damn thing.
Sometimes, the drunk driving (even if it leads to a DUI) is essentially harmless. No one is really hurt in cases where the driver is caught and/or wrecks their car and injures themselves. Oftentimes, plenty of drunk driving continues on, never resulting in a DUI. Sometimes, the exhausted and dangerous cop may make a boneheaded error (we're all human!) but just go about their lives, no harm no foul. No crime was recorded, or could be levied in either of these situations.
But in both cases, you introduce complicating variables into the pathway of these potentially dangerous weapons, like a van full of nuns driving orphans to an annual orphan gathering, or a dude chilling in his own apartment that has no reason to expect an exhausted and dangerous cop to barge in. Now, we have some potential for a crime!