For my story, I did some research before and found out that legally the police wouldn't have any grounds to tap the villain's phone, to record any conversations and get evidence. However, there is another character who is after the villain, with means to kill him the police highly suspect. Perhaps the police could use this to get creative. What if the police came to the villain, explained that they found out someone is after him to kill him, and the police ask for permission to tap his phone to try to catch the guy, in case any mysterious strangers contact him, that could be the man after him. The villain then agrees, but he of course would not use his regular cellphone to have conversations with other criminals. He would use one of his burners. But the cops tap the burner phone instead, and the villain doesn't know that they have tapped his burner, thinking they tapped his cell that is actually registered to him, that he gave the number of, to the police. Can the police trick someone that way, and tap one phone, when the suspect thought, they were going to tap another, especially if the suspect was in real danger from another person, as a legal means to ask him permission to tap it?