It’s just off the wall enough it might be true.
Regardless, this was very well planned and carried out. It required a lot of cash and access to weapons not easily acquired. He had to be in good shape physically, trained to use the firepower he had and be able to maintain his cool for the weeks and days beforehand.
It would seem extremely unlikely he could do all this by himself. Possible, of course. Probable? I don’t think so.