Registration. Case No. 67 “Hunt for the Echo”

Registration. Case No. 67 “Hunt for the Echo”

The police received a call. On the other end of the line, a man’s voice said:
“This is the echo of two recent explosions speaking to you. If you want to prevent another one, you’d better hurry.”

Why have these people become the target of an unknown bomber?
And how exactly does he operate?