Ask HN: Have there been instances of US fed govt acting on illegally gained info?

Asking this question in direct relation to the Snowden leaks. As it's all come out with how the NSA, FBI, CIA, etc have been massively overstepping their legal surveillance - are there any incidents of them actually taking action based on illegal surveillance of US citizens? I'm NOT saying it's a good thing or that it shouldn't be stopped - but just curious as so far it seems most people are saying "They see/hear everything which could/would be an issue down the line so we need to reel this in now". So, has the federal US government used their illegal surveillance to actually catch & prosecute any US citizens (that we know of)?