I used chipmixer in March. I thought the private key he gave me would be deleted, but it turned out that it was not deleted. On March 16, my btc was transferred by the police. I didn't commit a crime, it's just for privacy, so is there any way to recover my btc 
If you can provide all the documents and very good reasons why you need to use Mixer then go proceed to present your case, but you will be investigated and worse they will charge you if they see something illegal in your transactions, this will be too much work and too much time spent and you will have to spend money to get a good lawyer, not just an ordinary lawyer, but a lawyer that knows how Cryptocurrency works and this is quite costly.