As things stand now, obviously not. Law enforcement doesn't have to prove you did it before the search and seizure, merely establish "probable cause". Was it

As things stand now, obviously not. Law enforcement doesn't have to prove you did it before the search and seizure, merely establish "probable cause". Was it probable it was your computer doing the downloading? At trial (in the unlikely event it goes to trial instead of a plea deal), then it's supposed to be "beyond a reasonable doubt", but by then everybody (except in the number of cases involving Brady violations) sees everybody's cards. Except the Court believes the law enforcement officials as to what those cards say, even when it's not what they say. And that's the trouble: not in evidence gathering but in convictions. Network routers and modems are really bad at logging who accessed what from what MAC address. Mandating that routers start logging would in practice probably aid civil liberties more than harm them, simply because of the presumptions out there.