If police stop you illegally but then discover you have an outstanding warrant, any evidence found during the resulting search may still be used against you. An outstanding warrant can 'purge' the illegal stop's taint.
Evidence discovered during an unlawful stop may still be admissible if the connection between the illegal stop and the discovery of the evidence is sufficiently attenuated — here, by the discovery of an outstanding arrest warrant.
Narrows the exclusionary rule's protection. Outstanding warrants can turn an illegal stop into a legal one in terms of usable evidence.
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