In the US people have a right to face their accusers, to cross examine witnesses, to shake out lacking credibility or perverted motivations. If parallel constr

In the US people have a right to face their accusers, to cross examine witnesses, to shake out lacking credibility or perverted motivations. If parallel construction is being used to conceal people who testified against you there might be a motivation for it that is more complicated than an outright end-run around your civil rights, but it's not clear that it's any more justified. Moreover, even if there is something that ought reasonably be protected misleading the court about it isn't the right way to do it: Say there is a confidential source. Let the court decide if the results can be admitted and under what terms. Allowing prosecutors to lie isn't the right answer, the state is already at a tremendous advantage without it being dishonest.