Virtual CSI is designed in a way that every player may also become a mod of the community. Technically, the game is not really moderated. However, to create the feeling of a real investigation, a game master is needed to take on the roles of the suspects and witnesses. The game master is always the author of a case, which sadly means that he/she may not participate in the investigation of that specific crime.
As said above, every player may become an author. You simply have to scribble down your case idea in a comment below (all comments are screened) and if it has the feel of a CSI episode and is suitable for the game, it will be posted as an individual crime scene.
Your next step would then be to take control of all the non-player characters of your case. That means all witnesses at the crime scene, all suspects and of course the perpetrator. You also have to provide the group of investigators with any information that can be gathered through evidence analysis.
When creating a case for Virtual CSI, you need to have a type of crime. It does not necessarily have to be murder, though this is the most standard case seen in the tv series. Besides the crime, you need of course a victim and a perpetrator. Perhaps some other suspects and some witnesses.
If you need crime scene material or inspiration, just google for crime scene images. There are tons of photos, real and movie, in the internet.