The Scenesters (2009)

Wallace Cotten, a self important artsy filmmaker in need of income takes a job as a police crime scene videographer.  When his editor Roger sees the footage, he tells Wallace that it's the worst thing he's ever shot and vows to direct him at the next murder scene.

While there they meet Charlie, a crime scene cleaner who notices some clues that the police have overlooked.  The victims are all hipsters and Charlie believes they were all killed by the same person. While the filmmakers liken him to Sherlock Holmes, Charlie tells them that he just watches a lot of CSI.

Wallace and Roger come up with an idea to help their film careers, since business has been slow.  They decide that instead of telling the police what Charlie seems to have uncovered, they will use this as an opportunity to make a documentary about Charlie solving the murders.

The exposition is offered by a voice over in a film noir style - which reminds me of the descriptive qualities of old time radio shows - and also by trial scenes where the prosecutor (played by Sherilyn Fenn) questions the filmmakers and Charlie on the stand.

It's a dark comedy and there are some funny scenes, but it's fairly uneven.