Little Sister - Pieter Vos, Amsterdam, Book 3

Her death will haunt us forever. Now the price must be paid.
Kim and Mia Timmers were ten years old when they were accused of murdering the rest of their family and the lead singer of the world famous band, The Cupids. The evidence seemed irrefutable at the time, and the sisters, who have been in a Marken institution for ten years, are now due for release.
Pieter Vos, DI in the Amsterdam police, is given cause to re-open the case when the girls disappear along with a nurse who was supposed to escort them to a half-way house in Amsterdam. As the police investigation continues, it soon becomes evident that there is more than meets the eye at Marken, and senior staff at the institution are beginning to panic as they fear certain secrets might come to light. Even Vos's boss, De Groot, seems to have something to hide which is relevant to this case.
When the dead body of the nurse washes up on the beach at Marken, and the case takes a different turn as the various...