A serial murder case, the police and his forensic doctor rushed to the scene of the crime, only to find that the murderer left nothing but a dagger, not even fingerprints. It seemed that this was an almost perfect murder case. The only clue was a dot on the hand of the deceased. Everyone would have a dot on their hand, but it would become one dot or two dots as the number of people increased, which only made all the policemen in the police station feel very annoyed. It was only in the end that he discovered that the killer was the sister of his medical examiner.
Intention: I don't know