My comment about modern government surveillance techniques was a general one. No one can deny that government's today can and do use mass surveillance techniques on the public. And the government does everything it can to conceal those activities.

Within that greater surveillance regime we have the government employing secretive methods to investigate alleged crimes. But whereas the government can do almost anything it pleases with mass surveillance- because it doesn't need judicial review- it must reveal its methods in a criminal trial. If it doesn't, then the evidence can't be tested for its accuracy and legality. And evidence that can't be tested by council is virtually worthless in court.

Having a judge's approval to wire-tap a phone doesn't prove that all the evidence submitted was gathered lawfully. Each piece of evidence is subject to careful examination in court.