He certainly had nothing to do with acquiring the paintings.
This guy is a hermit who inherited the collection from his parents and (from what I’ve read) never learned to love anyone or anything except “his pictures.” It seems pretty clear that something is a little off with the guy, but I don’t think he had malevolent intentions. It seems more likely that he just suffers from some combination of extreme selfishness and/or paranoia.
His father was a modern art expert and one of the few art dealers allowed to traffic in “degenerate” art during the Third Reich, when he probably acquired most of the collection.
And even his dad may not have done anything wrong per se. He almost certainly benefited from Nazi policies (both general bans on “degenerate” art and confiscation of Jewish property) that made it difficult for others to hold onto these artworks, But he wasn’t the source of the duress that made others give them up. It’s very hard to know whether he was a greedy Nazi collaborator opportunist who took advantage of others’ duress to amass a spectacular collection of his own. Or whether he was a selfless savior, spending his own money to preserve works that the Nazis might otherwise have destroyed. The truth is probably some combination.
