The Hanging Girl by Jussi Adler-Olsen

When Carl Morck, head of Sweden's Department Q where the coldest of cold crimes go to die, receives a call from a colleague on a remote island, his first instinct is to put the man off.  That is always Morck's first instinct and when he finds out the man is calling about a case that is twenty years old he is definite about not wanting to get involved.  When a stunning event happens to the detective who called the same day, Morck is reluctantly pulled into the case.

The case concerns the death of a teenage girl who was found hanging from a tree after a hit and run accident so forceful that she was thrown up into the tree.  She was found by the policeman who spent the rest of his life consumed with the quest to find out who hit her and left her to die.  After twenty years, what chance is there that a road accident can now be solved?  Still, that's Carl's job so he and his assistants Assad and Rose head to the scene.  They find out that the girl had recently come to a school there where she made quite an impact with her beauty and flirtatious manner.  Right before her death, she seemed to have moved her interest to a mystery man not connected with the school.  After studying the case, the team believes finding this man will be the key.  The only thing they have to go on is that he was a good-looking man who was fascinating to women and that he was interested in the old religions that worshipped the sun.  Is it even possible to find him?  Most would give up but that's not the Department Q way where once something catches Morck's interest, he cannot give up until he finds the truth.

This is the sixth installment in the Department Q series.  Fans will be delighted to spend more time with the Department Q staff, now enlarged with the addition of a new man, Gordon.  Carl is fascinating, reluctant to get involved but unable to put a mystery aside.  Assad is enigmatic and constantly surprises with his hidden abilities.  Rose has her issues but is a marvel of organization and the sparkplug that forces the men to never give up.  This book is recommended by mystery readers.