Might be wrong about this, but I believe how it works in practice is that a tax return just can't be used as evidence in a court of law (for non-tax related rea

Might be wrong about this, but I believe how it works in practice is that a tax return just can't be used as evidence in a court of law (for non-tax related reasons). So if the FBI just so happened to obtain these tax returns through some means, then found /different/ evidence, then using that instead would be fine. https://en.wikipedia.org/wiki/Parallel_construction https://en.wikipedia.org/wiki/Parallel_construction