It seems to be setting it up that yes, he was a Nazi, and that she stumbled on his identity incidentally. After seeing/studying the pictures and the histories, she implanted a fictitious memory.
That said, between monsignor's and Arden's own reactions (plus the shit in his apartment), it's still very possible he WAS a war criminal.
That said, between monsignor's and Arden's own reactions (plus the shit in his apartment), it's still very possible he WAS a war criminal.