There is indeed a fairly strong case. Mallory's body was found a few years ago in a position and in a condition which people have suggested shows that he was on his descent. The last time that they were seen alive, they were very close to the summit and there's certainly no reason to think that they didn't reach it. This isn't a brilliant source, but it gives the basics quite well. http://surviving-history.blogspot.co.uk/2012/12/a-corpse-of-everest-deadly-final-hours.html