The Hanging Girl, by Jussi Adler-Olson

Carl Mørck, head of the merry band of misfits called Department Q, heads to the Danish island of Bornholm to investigate the cold case death of a school girl found hanging from a tree.  Adler-Olson is great. 

Conspiracy of Faith, by Jussi Adler-Olsen

Adler-Olsen is pretty amazing.  He writes with humor and heart, and as chillingly and creepily as I can stand. In this case, there isn't much of a mystery as you are in the head of a serial killer from the start. He is damaged, smart and pretty much a cunning wild beast.  He comes to the attention of Carl Morck's Department Q via a 12 year old message in a bottle, written by one of his earlier victims.  Carl, Assad, and Rose each bring their own unique skills to the chase.  Love this series.

The Absent One, by Jussi Adler-Olsen

Carl  Mørck, head of Copenhagen's cold case Department Q, now has two very capable, very odd people working for him, Assad, a civilian police employee who doesn't seem to get the difference between being a police officer and a civilian aide, and Rose, who is bossy, moody, and snippy, but wonderfully resourceful and capable.  They start out investigating the 20-year old murder of a brother and sister and find it linked to a long list of brutal attacks.  Powerful forces are out to stop them, by any means necessary.  The good guys are a hoot, the bad guys a little over the top. The Danish title was Fasandræberne, meaning Pheasant Killers; the UK title was Disgrace; and the US title The Absent One.  There's something a little odd about that. I want to read his last two:  Message in a Bottle and Journal 64.

The Keeper of Lost Causes, by Jussi Adler-Olsen

A pretty interesting book, told from two perspectives.  Some chapters are told from the viewpoint of Danish Deputy Detective Superintendent Carl Mørck, who has been made the head of Department Q to deal with high profile cold cases and to keep him out of trouble.  He is given a basement office and a Syrian assistant, who magically makes things happen.  Mørck is tormented and has difficulty with authority, and his parts of the book have humor, sorrow, and brilliant police work.  The remaining chapters are told from the perspective of Merete Lynggard, who is kidnapped and tortured, physically and psychologically, for five years.  These chapters are gruesome and difficult to read.  I'll keep an eye out for translations of Olsen-Adler.  Also published under the title Mercy.