In my story, it's a thriller where the MC, a cop, uses unorthodox methods to catch a gang of crooks. He has found out who the leader of the gang is possibly, by hacking into the personal information of a lawyer he hired to defend one of the others. After hacking into the lawyer's info, he finds out the leader's identity, and then starts tailing him for weeks to see what crime he may commit next. He is following him and watching him meet up with the others from afar with binoculars. As he is watching them from afar, he sees the gang leader murder another person. He cannot stop it in time cause he is too far away. Now if he chooses to go after the leader and arrest him, according to lawyers I researched info from for the story, they said that his testimony will be inadmissible in court, because a cop cannot testify to someone's identity, if the identity was obtained through the commission of a crime, in this casing, hacking. So if he says he saw a murder, and they ask him who the killer he saw was, if he says how he knows him through hacking, the evidence is then tainted and inadmissible, since the leader's fourth amendment rights were violated to discover his identity as evidence, through the hacking. So since he cannot tell the police how he found out the leader's identity without his testimony becoming inadmissible, what would his next move likely be, after failing to stop the murder in time? Thanks for the input. I really appreciate it.