This is a horrible, horrible film. So why have I given it 4stars? Well, that's because this should be a horrible film, the subject matter is truly disturbing. This is not an easy watch. It is extremely creepy and unsettling. However it has been well written, acted and directed.
It is certainly not a film you could watch over and over. It is quite slow and you sort of know what the plot is going to be straight from the start. However you are drawn into the film and you do want to stick with it to the end to see how it goes.
One thing I would say is that there seemed to be a lot of characters in the police that you didn't really get enough information on them, there is a pregnant woman who seems to have a story there somewhere but it is never told. I suppose this would have taken away from the main story but it might have been better just having one or two police at the most so that you could focus more on them, e.g. the older retired policeman struggling with the case he could never solve and then the newer policemen wanting to solve both cases and not repeat the mistakes of the past. I also had some difficulty, especially at the start in telling the difference between some of the characters and this made the plot slightly confusing!
Overall, it is worth a watch, it is slow but also powerful and dark, good acting and well directed. It would probably have been better as a tv series rather than a stand alone film. This would have given more time to build up the plot and get to know the policemen and their back stories. The end is a bit frustrating and you might find yourself shouting at the tv in anger as the credits roll. However, I suppose the ending does sit with the whole unpleasantness of the film, as I said before this is a horrible, horrible film so don't expect a happy ending, or even one that resolves the plot.