British detective TV show name and episode

Hi!! I’ve been thinking of this for 15 years and NEED to find for my sanity.

There was a detective/police show that I watched an episode of as a young kid on British tv probably BBC something. The show is for adults. It was contemporary at the time (2000s). Even as a young kid I remember thinking the way they solved the murder was kind of ridiculous but here goes…

From what I remember, there are 2 police detectives trying to solve a murder. I think one was a man and the other a woman. The way they solved it was because the murderer (I think) was a photographer. They had this picture he had taken of a house and a tree and using the Fibonacci spiral it was placed over the photo and the dead body (I think a girl) was found buried at the center of where the Fibonacci spiral was over the photo, which I think was under the tree.

Thank you for any suggestions!!