Okay, if you go by this, from the article;
“Hundreds of thousands of persons were confined under horrific conditions at Dachau and Buchenwald on the basis of their race, religion, national origin or political opinion,” said Assistant Attorney General Alice S. Fisher of the Criminal Division in a release.
“By commencing these proceedings against a man who participated in the victimization of those who were interned there, the Justice Department continues to make good on its pledge to ensure that the United States does not become a sanctuary for human rights violators.”
“The SS committed mass murder at Dachau and Buchenwald and subjected thousands of inmates to slave labor, starvation, grotesque medical experimentation, and torture,” said OSI Director Eli M. Rosenbaum, whose office investigated the case.
“The brutal concentration camp system could not have functioned without the determined efforts of SS men such as Paul Henss, who, with a vicious attack dog, stood between these victims and the possibility of freedom.”
There are in fact, many soldiers in different armies' all over the world who are guilty of the same thing. Yes, he was a guard; No, he wasn't the officer ordering the valves turned on in the gas chambers. Taking orders, no matter how distasteful, is something that a soldier does. Using the reasoning that current Nazi hunters' use, even the pastry chef for the camp commandant is a 'war criminal'.