Unless I'm mistaken, what kji is trying to say is that the police likely wouldn't use the BTC as direct evidence. More likely, the investigators will use the transaction history to draw up a list of potential suspects, which will include you and a bunch of other people who have nothing to do with the drug transactions. Then, they will dig further into each suspect using standard, existing investigative techniques. They'll narrow the list to a few suspects (including you) and gather evidence in the "traditional" way (surveillance, phone taps, paid informants - whatever they currently do), and finally arrest you based on that evidence.