To my knowledge, no (if you mean a blog post in which he explicitly states it). I'm just inferring from the disbelief and shock he apparently experienced when prosecutors chose to follow through.
If you mean if there was evidence whether he was wrong about the legality of distributing JSTOR documents...there seems to be some confusion about it, but it doesn't seem that many of Aaron's most legally-mindful defenders have said that freeing JSTOR was just as non-criminal as freeing PACER.
It should be noted, that you can login to JSTOR and read much of the content freely now. Albeit - only three articles at a time in your "bookshelf".
I wouldn't find it at all surprising if the various universities/journals/research bodies figure out how to make this research, much (majority) of which has been paid for by the public, available to the public.
I am one of the most "pro-ip-protection/opposed to copyright infringement" people on HN, and look down on anyone who violates producers/authors rights on commercial content - but I firmly stand with Aaron on the "Make research knowledge free to everyone" side.
If you mean if there was evidence whether he was wrong about the legality of distributing JSTOR documents...there seems to be some confusion about it, but it doesn't seem that many of Aaron's most legally-mindful defenders have said that freeing JSTOR was just as non-criminal as freeing PACER.