> Can we really say "You only obtained his fingerprint for the purpose of identifying him, you can't use it to unlock the phone"? That seems to me to be a very

> Can we really say "You only obtained his fingerprint for the purpose of identifying him, you can't use it to unlock the phone"? That seems to me to be a very reasonable thing to say. It seems to me that we have plenty of mechanism in place to say "you have X, you can use it for Y, and not Z, because using it for Z violates someone's rights". As a super contrived strawman example, if your computer ever gets confiscated by law enforcement, while they may be permitted to search it, they can't just play Fallout 4 or mine bitcoins on it. Another instance I think is similar in concept: juries are instructed to disregard things (i.e. pretend they don't have a piece of information for the purposes of a trial) all the time, when access to this information would be improper.