Where does “真犯人” come from?

真犯人 (Japanese) comes from Japanese 真, from Chinese 似.

真犯人 (Japanese): the true culprit

Definitions

Step	Language	Word	Meaning
1	Japanese	真	truth, reality; truth, reality, genuineness;...
2	Chinese	似	—

真犯人 — Etymology, Origin & Word History | Etymology Explorer