It would appear to me that they had to allow the crime to happen in order to indict and convict the perp right? And also allow the victims to bring suit for damages if they choose to.
The difference would be that they knew what the perp would do and let it happen, knowing the perp would find nothing incriminating (forcing perp to compose/construct evidence.)
Give Schiff enough rope to hang himself? That seems a bit like giving Homer Simpson enough donuts to shut him up! :^)