Confessions of a Madman

Confessions of a Madman is a cosy mystery/crime series of four books, literally about confessions of a madman, or is he really mad? Maybe his confession is true and some strange crime is happening. These books are available as a box set and individually. You need to read all four to complete the story.
Amanda and Jade, two policewomen who work in different towns, but who have been friends for years, meet for a friendly chat. By chance they each tell a story of a strange confession they had to listen to. Both unbelievable confessions are just about identical. This immediately makes one thing obvious to them - there has to be a criminal somewhere doing something no one had ever heard of before. The two confessions are too alike for it to be a coincidence.
Their first problem is to prove these two incidents were committed by the same person while showing beyond doubt it isn't some sort of elaborate hoax.
As the story follows the investigation, the women hear more about some of these 'mad confessions' and go on the trail of the man responsible. Eventually all the pieces start to fall into place, but there is one thing they can't get a handle on, no matter which way they look at it. That is how the criminal chose his victims.
In the last book, a policeman goes undercover to try to catch the criminal, but things do not go according to plan and he gets kidnapped.
Very slowly bits and pieces start to narrow down who the kidnapper might be, until eventually a well organised sting lets them catch him and find out why and how he did the things he did.