In fact, he want to hint to a previous victim, not yet discorvered by the police (and the police will think he is hinting his next target)
I wrote a lot of weird stuff in the crime scene So,I'll use one of them later to be revealed as a hint... I'm trusting my future brain .
Yeah 20 days later, I still didnt find the good way to do it. But at least I'm not bothered anymore