Responses

It's actually the duke if you have read the spanish-trans which is up to chapter 37 it confirms that the duke is the serial killer and killed louis look alikes . (Also the duke had drugged Louis so he could sleep with him. This is why louis was so obedient and didn't even seem drunk at the start) GREAT GUESS THOUGH- I started to doubt the author of the manhwa. ╮( ̄▽ ̄)╭
The killer is OBVIOUSLY Sabrina. Sabrina, is obsessed w Louis, as we know from the words,‘I’m worried about you’ as we saw Sabrina randomly appear in the princess room, we can safely assume she has been stalking Louis for MONTHS, and even became part of the guard to what? To have Louis get her pregnant *gasp! Why is this case going no where? Why can’t they find the killer? Because Sabrina is behind the office WIPING THE EVIDENCE!! When black cloak appeared tell me, where was Sabrina? How did Sabrina know Louis was pregnant? Because she stalked him the night prince and Louis preformed the devils tango, and as we know these murders have been going on for 4 months, so she began killing Louis lookalikes in hopes to satiate her rage and, because she wanted to draw Louis attention away from the prince!! Sabrina possesses all the power to murder and slaughter, and I’m sure has resources to bribe that man as she is Louis right hand woman or should I say... left hand woman seeing how she is everywhere Louis is... don’t bother calling me a genius, I’m well aware ╮( ̄▽ ̄)╭