The Absent One by Jussi Adler-Olsen

The Absent One: A Department Q Novel - Detective Carl Mørck finds a cold case file on his desk that the department considers closed.  A sister and a brother were murdered while playing trivial pursuit.  A suspect confessed to the crime and is serving his sentence.  However, when Mørck begins to investigate, he learns that there is more to the case.  But, he is ordered to stop by those high in the police force.

Kimmie, a suspect in the case is living on the streets.  She is determined to get revenge on certain men who hold high positions in the corporate world and society.  These men are just as determined to find her and eliminate the risk she represents.  All of them were involved in the case that Mørck is now investigating.  And all of them went to the same private school.