I've actually got a biography of him on my own book shelf, although I haven't read it in ~20 years. I'll see if it draws any conclusions on the matter.
So, kicky, here's the biography I have: https://www.amazon.com/Porter-Rockwell-Richard-Lloyd-Dewey/dp/0929753232/
I looked up the relevant chapter last night, and it comes down quite strongly on the "Rockwell didn't do it" side. So I guess we're down to dueling experts and I don't have a way to judge whether your biography of mine is superior. I suppose I could make a list of the evidence the book presents arguing against Rockwell's involvement, but I don't have time right now.