Can illegally obtained evidence be used to impeach a witness at trial, and can it impeach a non-defendant witness?

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The key idea is that there is a limited impeachment exception to the exclusionary rule: illegal evidence can be used to test a defendant’s credibility, but not the credibility of other witnesses. This is the rule you’ll see in Harris v. New York, where a confession or other illegally obtained statement may be offered to impeach the defendant’s testimony, even though it couldn’t be used as substantive evidence against the defendant. The purpose is to allow juries to assess the reliability of the defendant’s own account without letting the tainted evidence become substantive proof for others, which would undermine the deterrent effect of keeping illegally obtained material out of trials.

So, the best answer is that illegally obtained evidence may be used to impeach the defendant, but not a non-defendant witness. The other possibilities fail because they either insist on a blanket prohibition (which Harris rejects) or extend the tainted evidence’s use to all witnesses or to every kind of statement without the same limiting principle. The restriction isn’t about requiring a warrant; it’s about whose credibility can be affected by impeachment with tainted material.