Specifically, I'm wondering why, when confronted with the sight of the real Beast at the trial, Lazne doesn't recognize that it is not the creature his posse wounded and chased into the bog, or that it does not have to appropriate shoulder wound from the caiman bite. Is the Shambling Man skin intended to actually be a convincing likeness of the Beast? Or is Lazne keeping his doubts to himself?
Well, several months have passed since that incident, which leads to dulling of memory. Second, who knows what the long term effects of chewing swamp weed are. Also, the event Lazne remembers was at night. Was he carrying a torch himself? Did he really get a good look? How far were the hunters from the Beast? Finally, there are no stats presented for Lazne, so his INT and WIS are really up to you. Perhaps he is just a miserable old coot mired in prejudice who wants to see the Beast burn. Someone needs to be blamed for what happened. This could be a fun opportunity for you to role play him as a stubborn curmudgeon who has no doubts about what he saw that night dagnabit!
Lazne probably got a good look at him through the dark, so I made sure that everyone who had seen the beast saw its hands. In my game the Beast had one dragon claw and a choker's hand-- the Shambling Man skin looks extremely similar to the Beast, and Vorkstag has modeled it even closer from witness accounts of the Beast. The only real difference is that the Shambling Man has a human hand and a curled tentacle claw.
In either case, I had Lazne be both old and unable to produce real concrete details, claiming that it was very dark and he wasn't really able to get a great look at it. My hands idea tipped the PCs off far quicker than I would have liked, so if I had to run it again I would try to be much more subtle.