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 
I'm sorry for your loss but I think you should move on, the Bitcoin was seized on CM might be possible that it may be subject to forfeiture proceedings, which would make it difficult to recover. Even though you weren't obtained through illegal means but in the eyes of those who seized ChipMixer was illegal or include criminal activities and the reason they shut down the service. How big it is that you still wanted to recover? If that is so, it's better to consult a qualified lawyer for this.