When in doubt, blame the butler.
In all seriousness, though, how about we try something along the lines of...Everyone that signed in gets a turn for trying to make a mystery for our detectives. When being the criminal, the said RPers will have his detective put aside from the investigation for whatever reason and then proceed to be responsible for describing all of the crime scenes and suspects that the players will investigate.
It will be that RPer's challenge for, at that moment, try to be as descriptive as possible, detailing places in the crime scenes where the detectives could...Well...Detect clues and changes in the behaviour of the suspects which would allow the player to guess whether the suspect is lying or telling the truth. In case the current crime reveals itself to be too hard for the players or maybe shows a few flaws in it's logic or whatever, the current "Crime Lord" can choose to either try and fix up the problems by changing a few things or he can choose to pass his turn over to the next person.
"I may not agree with what you say, but i will fight to the death for your right to say it." -VoltaireYOU. YES YOU, DO YOU LIKE ROLEPLAYING? DID YOU KNOW RRR HAS IT'S OWN ROLEPLAYING FORUMS? DO YOU KNOW IT'S QUITE AWESOME? YOU SHOULD JOIN! YES, THIS IS SHAMELESS ADVERTISING. NOW CLICK THIS LINK.