The Immortal Game • 2016 rpg

Play a game of chess.

White: mysterious serial killer
Black: Detective Black

Black:

Pawn: Victims; no relation 

Rook: People that you aren't intimately connected with but you have always viewed as rocks

Knight: Contacts who regularly put themselves at risk for you

Bishop: Your cop partners

Queen: The person you are closest to

King: You

White:

Pawn: Clues

Rook: People who have provided you with shelter

Knight: People who idolise you

Bishop: You (Your identity isn't revealed, but Black sees you)

Queen: Your modus operandi

King: You

Be creative with your interpretation of the pieces.

Scenes
If white takes black, the person that piece represents is killed. If black takes white, Black gets a little bit closer to finding White through that piece. The person who took a piece gets to set up and act out/narrate a scene. The other player can optionally start a scene following that.
If Black checkmates White, they are arrested.
If White checkmates Black, White gets to do what they want to Black.
If there is a stalemate, Black finds out who White is but can't make the arrest.
Narrate the conclusion until you feel everything is resolved.