Disgrace by Jussi Adler-Olsen

Second Hand 

Detective Carl Morck of Department Q, the cold cases division, has received a file concerning the brutal murder of a brother and sister twenty years earlier. A group of boarding-school students were the suspects at the time - until one of their number confessed and was convicted. So why is the file of a closed case on Carl's desk? Who put it there? Who believes the case has not been solved? Carl wants to talk to Kimmie, a homeless woman living on the streets of Copenhagen, but someone else is also asking questions about her. They know she carries secrets certain powerful people want to stay buried deep. But Kimmie has one of her own. It's the biggest secret of them all. And she can't wait to share it...