Yea, there would have to be compelling evidence of something he specifically did or he would have to have been in pretty high leadership, imho. Just being there is not enough.
Trying to convict every hoodwinked foot soldier just because is not a precedent to set, else everyone who has served in the US is at risk if the wrong sorts come to power.
An important point. At this time, I doubt if anybody who was actually in a decision-making capacity in the camps is still alive. All we have left are people who were young conscripts at the time.
Soon even they will have passed on, and the Nazi hunters will have to find new jobs.
According to the article, German law has been changed so just being there is indeed enough. The rationale being that since the only purpose of the camp was murder, being there makes you a murderer.