Blue Circle People

In the middle of the night, blue chalk circles appeared continuously on the streets of Paris.

There are discarded sundries such as beer bottle caps, vegetable boxes, shoes, magazines, hats, etc. in the circle, which are different every time, and the same sentence is written on the side. Is this a quirky prank, or is there some other conspiracy?

Sheriff Adamsberg's Investigation

Sheriff Adamsberg thought the matter was strange and felt that something unusual would appear in the circle. While he sent people to investigate, he arranged to guard, and sure enough, corpses began to appear in the circle; at the same time, Adamsberg and his assistants also tracked down some clues, but the real murderer had to go deep into the danger and be caught after rigorous reasoning.