It is a very particular novel by Jeffery Deaver since none of his usual characters intervene.
It is not part of the Lincoln Rhyme saga with Amelia Sach nor is it part of the successive saga with Kathryn Dance or the current one with Colter Shaw.
It is a book that is part of the "independent" bibliography of Jeffery Deaver.
It is about a Nazi war criminal, Hitler's rise to power and the crimes of humanity committed by the Nazi regime.
I read it when I was living in Italy under the title (in Italian) of Il Giardino delle Belve.
It is a very very good book, thanks for commenting @stevenson7.