WASHINGTON — The 89-year-old Johann Breyer shuffled unsteadily into a federal courtroom in Philadelphia on Wednesday morning, using a cane for support as he sank slowly into a chair at the defense table.

The retired toolmaker from what was then Czechoslovakia, who immigrated to the United States in 1952, was thin and pale and dressed in a green uniform after a night spent in jail following his arrest at his home in Philadelphia. He looked confused at times, too, but when the judge asked him if he understood why the German authorities wanted to put him on trial there, he answered simply, “Yes.”

Nothing about his demeanor suggested the long-ago secrets that the authorities in both Germany and the United States say Mr. Breyer has carried with him for 70 years. As an armed guard at the Nazi concentration camp at Auschwitz and a member of the notorious SS “Death’s Head” battalion, the authorities charged on Wednesday, Mr. Breyer was complicit in the gassing of 216,000 Jews taken there in 1944 from Hungary, Czechoslovakia and Germany.

The Germans, seeking to have him extradited to stand trial, have charged him with 158 counts of aiding and abetting in murder — one count for each of the 158 trainloads of Jews taken to the killing center at Auschwitz in a six-month span. Most of the so-called deportees, including many thousands of women, children and old people, were killed in gas chambers almost immediately after arriving at Auschwitz, with their bodies burned in four crematories.