Interlogue problem, where to put it?

so i am writing a noir story and i wanted to introduce a occultist character. i made a backstory of his recent case to better introduce him but then got confused. i decided i will put a small Interlogue about the character in between the chapter.
so my question is should i put it before the main introduction but after like a little foreshadowing, or after the main introduction and story use, i think many of you will say after the main introduction. but i still want to ask.