Even though the act of performing that download is illegal, the individual has a right to his privacy until a court deems the information necesssary in a criminal case.

This is not entirely true.
Over here, EVERYONE who gets notice of a crime being comitted has the obligation to report this to the authorities. So if you're an ISP and you notice that one of your subscribers is putting child porn pics on his dedicated web space on your servers, you'll have to notify the authorities about it.
What the authorities do with that information then is up to them. If they decide to press charges, good. If they don't, they have to state a good reason.
If the crime is discovered later on, and they find out that you knew about it for some time but didn't take any action to report it, they can sue YOU. (granted, the chances of this happing are practically zero, but the law does state it)