https://www.theguardian.com/world/2017/jul/20/dutch-prisoners-cold-case-calendars-solving-crimes
Police received 160 tipoffs after trial run of calendars featuring unsolved murder
Prisoners across the Netherlands are to be issued with calendars for their cells featuring unsolved murders or disappearances as part of a drive by the Dutch police to crack unsolved cases.
The so-called cold case calendars will be handed to all 30,000 prisoners in the country after a trial run in five jails in the north resulted in 160 tips to the police.
Each week of the year in the brightly coloured 2018-19 calendars will be illustrated with a photograph of a missing person and details of the case. The hope is that many of those in jail will know details of some of the crimes or may have heard other criminals chatting about them.
Announcing the national rollout of the calendar, a police spokesman said: The experience of the police and judiciary shows that prisoners have relatively high levels of knowledge about committed crimes.
On their website the Dutch police said advances in forensic technology had made acting on tipoffs even in very old cases significantly easier. There are around 1,500 unsolved crimes classified as cold cases in the Netherlands.
There are two important factors that play a role in this, the police said. On the one hand there are developments in forensics, which offer the teams more opportunities, such as DNA. On the other hand, witnesses can play a crucial role. Witnesses who had seen something at the time, but did not dare to come forward, sometimes dare to do so over time
The idea of the calendars was borrowed from the United States, where every year several states distribute a deck of cards containing information about cold cases among prisoners.