The Killing Of Emma Gross: a detective novel about a true crime in the Weimar Republic

The Killing of Emma Gross - Damien Seaman Really couldn't see the point of this book. I read this because it was suggested as being similar to one of my favourite authors - Philip Kerr. Apart from being based set in Germany during the war it was nothing like him and very boring fictional account of an actual murder. Not sure what the purpose of the book was - why make a fictional account of a real murder unless it has some real historical significance like for example Jack the Ripper theories?