Welcome to the difference between evidence and intelligence. IP address has very rarely ever been used as evidence, but it is still enough to get a search warrant (during which time evidence will be collected), and it is still enough to get you put under surveillance. This precedent has already largely been followed in CP investigations, people who are raided based on IP address *intelligence* (ie: every single person busted with CP) almost always have charges dropped if no CP is recovered during the raid, but it has already also been established that an IP address *is enough probable cause for a search warrant* and nobody is going to get out of charges if additional evidence is found after they are raided / put under surveillance after they are identified by their IP address. "But the only reason they knew I was mailing heroin is because they put me under surveillance after they found my IP address!" is not going to fly. "But the only evidence they have that I am the one who sent them heroin is that they traced their communications with the person they made a heroin deal with back to me!" has essentially never been enough to get a conviction in court and usually the judge throws out cases where a traced IP address is the *only* evidence