I was shocked and saddened to hear of Hasan Niyasi's death (see some earlier blogs and http://www.3pipe.net/). I was contacted with him initially in connection with the Leonardo portrait of a young woman. He had an excellent grasp of the key issues and more logical good sense than many art historians. My subsequent contacts confirmed that he was a better art historian than a good number who are paid money for being so. We never met in person, alas.
I am currently in dialogue with a dealer about attributions (in general). I will see if he is willing for it to be posted in honour of Hasan.
Unlike Holmes, not being a pipe-smoker, I go for the three-coffee problem.