There are of course the extremely rare cases where they’ll pretend to press charges and use a grand jury to get them dropped (e.g. Torgalski & McCabe), and the even more rare case where the murder gains so much publicity that they’ll have to pursue a real case (e.g. Chauvin) or is so incredibly heinous and brutal (e.g. Michael Valva) but by and large police will never face prosecution.