This was probably the worst episode as far as the police mystery element of the show goes.
The break from the normal format of the show was bold I guess, in that we know who did it from the start and then the rest of the show just goes looking for the details to prove it and they never really manage it. It's solved in a gun point "drag the confession out of your executioner before the kill you" plot device.
This was bad enough but the 'proof' they conjour out of thin air didn't add up.
The victim being shot outside and then going into the room and locking the door would be fine except there was no blood anywhere, and the bullet exited and lodged in an outside wall!!!
Rooms with doors closed becoming sound proof rooms ignoring how loud gunshots are, this episode was well below the not very high standards we expect for the mystery element of the show.
To be fair most of us are not here for the brain teaser murder solving as we're never given enough info to solve it ourselves, yes it's the characters we enjoy and unfortunately in this episode the details were pretty clunky too.
I get that it was a reprise second send off for a cast member who we know in hindsight comes back gain soon, but it just didn't add anything much to the story that was enjoyable, and her whole arc was clumsy and badly written.