Not a lawyer, but my understanding is if they find illegal stuff during discovery for an unrelated charge, you can be charged for that as well. One caveat would be if the original search was illegal, so say you see some police in public and you start recording them, then they come and take your phone away as evidence for the crime of recording police, which everyone knows is not actually illegal. They did not have the right to take your phone to begin with so anything they find on your phone then should be not admissible as evidence against you. Again, not a lawyer.