[ngoede]

The existence of parallel construction is huge problem with the idea that the only result of gathering evidence illegally is that that evidence is excluded from legal use.

The police/NSA/whomever can still use that information to inform their investigations to discover other legal evidence that they could otherwise only have found by chance. Not to mention the possibility of just leaking information like this later to discredit or punish a political enemy.

[kevinnk]

I thought the "fruit of the poisonous tree" doctrine meant that any evidence that is found by examining evidence collected illegally still cannot be presented. The problem with parallel construction is that the police/NSA lie about the origin of their suspicion and avoid the "poisonous tree". (I should mention IANAL so please correct me if my understanding is wrong)