I don't think that's quite right. It was not that he did not know he possessed them, it was that he did not posses them even though they were in his browser cache
That's a great theory, but it doesn't seem to match up with what the ruling actually says:
We must consider, among other issues, the evidentiary significance of "cache files," or temporary internet files automatically created and stored on a defendant's hard drive, and the defendant's awareness of the presence of such files. We conclude that where the evidence fails to show that defendant had such awareness, the People have not met their burden of demonstrating defendant's knowing procurement or possession of those files.
The difference between viewing pornography on the Internet and possessing pornography may be illustrated this way: Suppose that word gets around a school that "there is a dirty picture in the third stall in the boy's room" and some of the boys make excuses to go and look. They do not become possessors of the picture. But one could become a possessor by taking the picture down, taking it home, and hiding it under his matress. And, if we assume (for purposes of argument) that what the boys did was wrong, what the last boy did was more wrong.
Thanks for the lesson but your analogy is off. Under NY state law, looking at that picture on the wall is not illegal (federal law is another story but not in play in this case) but taking a picture of it so you can look again without going to the stall (i.e. caching it locally) means you now possess it. But what if the kid who took the picture didn't know that he has the picture, didn't look at it again, and didn't even take it on purpose. Can he be said to possess for purpose of criminal prosecution? The court said no. Taking it home and hiding it under his mattress would be a completely different story.
What has happened here is the judges now understand what a browser cache is: a temporary storage area over which users do not ordinarily excercise control. It may be a storage container in a technical sense, but not in a legal sense. The fact that a document or an image is in the cache does not indicate that the computer's user is trying to keep it. The judges understand that something which would not be considered a crime if done using old technology should not accidently become a crime when committed using a new technology just because of some obscure technical detail of how the new technology works.
Yet in other cases where the defendant was shown to have manually deleted images from the cache and/or copied them to other locations, this same defense has failed. If you actually read the ruling (and others that I've linked in other posts in this story), you'll see that the critical issue is whether the defendant demonstrated that they were aware of the cached images.
In that case, the legislature may have to decide what level of repeated viewing incures the same guilt as keeping it. But this decision has to be made by the legislature, not by calling viewing possession.
Which is exactly what the judges said in this case. The state law speaks only to possession, unlike the federal law that wasn't used in this case. Rest assured that the NY legislature will update their law.