Police and state prosecutors publicly acknowledge (albeit implicitly in some cases) that they fail to disclose their frequent use of spoofed mobile phone towers in criminal cases, which is very much in violation of constitutional law on searches and law addressing disclosure in criminal proceedings. They assert they can do so because the Feds told them to. What other illegal surveillance are they routinely conducting and using in the service of prosecutions that they fail to disclose?
http://phys.org/news/2015-04-baltimore-police-surveil-cellphones-secrecy.html