To be honest my experience of forensics is based solely on documentaries and CSI, but something that seems important is taking lots of photographs. SL Viewers offer a free-roaming camera that you can position how you want, and a 'snapshot' feature to save screen-shots. So that's one tool ticked off.
Another common tool seems to be the UV light, for highlighting various bodily fluids. A representation of this is fairly straight forward in SL; you simply control the switching of textures and emissive colour (see the images below of the suspected escape route - a bathroom window).Note that it was the ladies bathroom, which already gives us a clue as to the muderer.
A major issue encountered is that OpenSim doesn't seem to allow objects in-world to hear messages from HUDs. In the example above the avatar is carrying a UV light, which you click on to toggle the light on/off. This method may be more realistic in that different tools must be worn in order to be used, but from a usability perspective a HUD is often the best choice. We'll see how this affects other tools.