The Constitution does not require the police or prosecution to preserve all potential evidence. The critical distinction is between evidence that is materially relevant and evidence that is potentially useful. Police loss or destruction of potentially useful evidence (i.e., evidence that might prove exculpatory if tested) does not violate due process "unless a criminal defendant can show bad faith on the part of the police." ¹ At the same time, loss of (or failure to disclose) material exculpatory evidence establishes a due process violation. ²

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