The heavy rain accompanied by strong wind had the result of hiding the clues that Inspector Jonathan Spalton needed to reveal the identity of the murderer. It was as if someone had taken a giant eraser and wiped everything away. The only thing that somewhat facilitated his investigation was that the murders had common characteristics and were all committed in the same building block. Besides the lack of clues, the inspector had to face public opinion, the governor who wanted to boost his popularity, the prefect who was collecting successes to use them in the upcoming elections, and the mayor. An entire mechanism that couldn't function unless Spalton caught the murderer red-handed, so that he could parade him around the city - always accompanied by the ruling class - like an attraction of a traveling circus.
It is always the detail that opens the door and pushes the murderer into the wrong path. And Spalton had the scent of a bloodhound and the necessary luck. Because luck is what determines our destinies.