Once We were Brothers  -  Ronald Balson
                   Historical Fiction

I have read a lot of H. F.  Most have moved me, many have saddened me, but this one brought me to tears.

Two young boys, one German, one Jewish brought up in the same loving Jewish home.  Then WWII  happened.
The story is told by Ben to his lawyer who helps Benn build a case against a very prominent man,  a man Ben suspects of being a former Nazi.

Goodreads:

The gripping tale about two boys, once as close as brothers, who find themselves on opposite sides of the Holocaust.

Elliot Rosenzweig, a respected civic leader and wealthy philanthropist, is attending a fundraiser when he is suddenly accosted and accused of being a former Nazi SS officer named Otto Piatek, the Butcher of Zamosc. Although the charges are denounced as preposterous, his accuser is convinced he is right and engages attorney Catherine Lockhart to bring Rosenzweig to justice. Solomon persuades attorney Catherine Lockhart to take his case, revealing that the true Piatek was abandoned as a child and raised by Solomon's own family only to betray them during the Nazi occupation. But has Solomon accused the right man?