Jussi Adler-Olsen - The Phantom Killers

The Phantom Killers is a crime novel by Jussi Adler-Olsen. The book is the second part of the Q-series about Department Q, which solves old cold cases. A police investigation team in Copenhagen that specializes in solving old unsolved cases is contacted by an anonymous sender who sends them two skulls. The police believe that the skulls are from an ancient grave, but it is not until the investigation of a collection of old cases that they discover what really happened...