The Redeemer by Jo Nesbo

An assassin is on the loose in Oslo. When he realizes that he's killed the wrong man, he becomes even more determined to carry out the job. To stop him, Harry Hole and his colleagues on the Oslo police force must delve into the lives of the victims--brothers Robert and Jon Karlsen of the Salvation Army. Harry also begins the task of tracing where the killer-for-hire is from, which leads him all the way to Croatia. In The Redeemer, Nesbo continues the adventures of Detective Hole and his co-workers, creating a complex police procedural that's hard to put down--once you get into it. The Redeemer, while not yet published in the U.S., comes in the series before The Snowman, which was just published. This is very frustrating, since there are important events in The Redeemer that help you appreciate The Snowman even more. That might be OK if The Snowman were a better book than The Redeemer, but that's not the case. Too bad Random House couldn't publish them in order!