One of Nessie's major witnesses, brazenly lying in court.
Yes, the identification of Demjanjuk was challenged in court and the witnesses found to be unreliable and unable to identify him. When a Nazi denied being responsible, his defence is able to challenge witnesses. That explains why in the other camp trials, witnesses were not challenged, because the Nazis admitted to the allegations and crimes. Demjanjuk denied responsibility or being there, but just like every other Nazi, he did not provide any evidence to challenge that gassings took place at TII, or for mass resettlement.