Very well done! I loved the concept of the game as well as the way you developed it. It is indeed a bit frustrating at the begining, but I don't see this as a problem. Real life detectives and police officers have to deal with A TON of frustration during investigations, and even more frustration sometimes in the Courtsof Justice. In this job, the devil is in the details.
The only thing I would add is a way to check out the people that you are sure are innocent, so the player can better focus the analysis on the remaining suspects - specially when you need to keep checking in multiple places.