There are 8 books in the Inspector Kurt Wallander series, starting with Faceless Killers.

Set in Sweden.

Man Who Smiled is #4 — easily the best so far.

After killing a man in the line of duty (in The White Lioness), Inspector Kurt Wallander finds himself spiralling into an alcohol-fuelled depression.

He has just decided to leave the police when an old friend, Sten Torstensson, asks him to secretly investigate the recent death of his father in a car accident.

At first Kurt dismisses his friend’s suspicions as unlikely, but then Sten is found murdered in exactly the same manner as a Norwegian businessman shortly before.

Against his previous judgement, Kurt returns to work to investigate what he is convinced is a case of double murder.

Wikipedia