Jason, I believe that your pictures contain a clue.
However, it is very helpful to look at a better resolution picture of the area shown in picture 2:
https://www.google.com/maps/@36.5782229,-118.2963799,168m/data=!3m1!1e3
This is a "google maps" picture, which can be zoomed without loss of resolution.
What is shows is that the Main Mt Whitney Trail, (marked on this picture as "John Muir Trail"--which is correct), is located very near to the north side of the summit plateau, quite close to "the easy walk off" route along the north side, and which can be seen in the photo.
A comparison with the "photo 2" which marks the site of recovery reveals that the site is
almost exactly below the sharp turn in the trail. It is a very sharp turn....almost 180 degrees, which would suggest to me a switchback. A very common error that hikers make, is to not realize they are at a switchback, and to continue on in a straight line. This is especially true going downhill. If he did that in confusion and partial light (he would be looking into the sun), it would take him to the edge of the north escarpment, where it would be easy to slip and fall.
If there is the evidence of him signing the summit register, then his fall would have been heading down, and I'm very suspicious that this describes his actions. It is possible that it could have happened on the way up, also, but I think that it would have been much more likely on the way down.
Amazingly, I believe that the videos that Steve C shot last week of that area of the mountain almost certainly contains the terrain in question. I believe that it would be in video number 7/8 in this thread:
http://www.whitneyzone.com/wz/ubbthreads.php/topics/39194/Whitney_Mountaineers_Route_Eas#Post39194I was particularly struck by Steve's commentary in video 8 in which he comments "I sure wouldn't want to be doing this with a full pack".
