That's not the only issue. Parallel construction is also a concern - a process where the government "launders" information received unconstitutionally, such as lying and claiming it was from a confidential informant; or using the illegally received information to give them insight into how to pursue building a "clean" line of evidence that appears to be from scratch but isn't, such as "coincidentally" stopping a particular vehicle for a traffic violation, when investigators know the vehicle will be breaking the law from their dragnet surveillance (e.g., smuggling drugs). In some cases, these agencies have lied to the courts about how they obtained their evidence.

> But instead of being truthful with criminal defendants, judges, and even prosecutors about where the information came from, DEA agents are reportedly obscuring the source of these tips. For example, a law enforcement agent could receive a tip from SOD—which SOD, in turn, got from the NSA—to look for a specific car at a certain place. But instead of relying solely on that tip, the agent would be instructed to find his or her own reason to stop and search the car. Agents are directed to keep SOD under wraps and not mention it in "investigative reports, affidavits, discussions with prosecutors and courtroom testimony," according to Reuters.

https://www.eff.org/deeplinks/2013/08/dea-and-nsa-team-intel...