You're not thinking it through. If the FBI sits back, they become complicit in whatever illegal activities were happening. Then you can have situations like t

You're not thinking it through. If the FBI sits back, they become complicit in whatever illegal activities were happening. Then you can have situations like the ATF gunwalking scandal (http://en.wikipedia.org/wiki/ATF_gunwalking_scandal http://en.wikipedia.org/wiki/ATF_gunwalking_scandal) in which the ATF was trying to track smuggled guns up to higher-level suppliers, and had one of those guns used in a murder. This would presumably go so far as the FBI asking other agencies to cease investigations which might compromise their larger operation. At some point, they will have to act.