But you see, he wasn't even told the offense. And neither have we. That's the magic of child porn - you'll never see a journalist trying to dig deeper into such cases.
Why would police suspicion of an IP address trigger any knowlege by a miscreant who uses said IP address? (While miscreants who know that they're being watched may do something, surely police can know a potential suspect's IP address and gather additional evidence without tipping him off.)
In any event, I was addressing the assumption that quick action is required as soon as the police know an IP address. It isn't.
As to the additional evidence, some indication that it was actually received at the guy's computer. After all, I'm pretty sure that the police don't raid the post office.