The major problem is parallel construction.
If the police can use this data - obtained illegally and surreptitiously using tools like accessdata or cellebrite to search for confirmation, they could extract a plea from you or find/manufacture other facts that do incriminate you or tear down your defense.
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Wouldn't they need to decrypt the data in the first place? But perhaps that digresses from the point...
The major problem is parallel construction. If the police can use this data - obtained illegally and surreptitiously using tools like accessdata or cellebrite to search for confirmation, they could extract a plea from you or find/manufacture other facts that do incriminate you or tear down your defense.