As a cop you were supposed to investigate your own crimes that you perpetrated as the wiseguy. It sounds weird but he claims they figured it out and it worked.
The only comparison that springs to mind is Fahrenheit/Indigo Prophecy in which the player takes the role of both the murderer and police. Initially I was tempted to play the police badly because the suspect Lucas was innocent, but the game won't progress without evidence, and missable clues are covered by alternate clues to ensure the investigation has enough for an arrest. If Lucas messes up before that point, it's an instant game over. We don't even get the pleasure of watching him explain to a courtroom jury that a wizard committed the murder while the amused judge pretends to call Gandalf on an invisible telephone.
The main issue with playing both sides and investigating your own crimes would seem obvious - you'd be constantly fed repeating facts, things you already knew. Fahrenheit tries to get around this by either having Lucas leave clues he wasn't aware of, or through editing trickery. Furthermore, Lucas is trying to solve the same mystery, it's just that his involvement is personal. So the two perspectives work in tandem to provide players with new information.
Regardless of how Vavra approached things, I would've loved to see his Mafia 3.