A VPN isn't a solution because it would only help the guilty. The innocent still fall victim to someone else jumping on their wifi and uploading stuff unVPNed.

There is also the highly probable case of the IP address being shared by many people or switching to a new user mid day which does happen.

Something as trivial as the police forgetting to check what timestamp their website file upload date is in could easily result in getting the entirely wrong customer from the ISP.