That was my 1st thought too he prolly hire someone to give it to duke but now that duke is gone I don't think we'll find out anytime soon but again wouldn't be surprised
The reason why I am sure that it was jurion because of that one panel of duke meeting the black masked dude about Jiwoo’s assassination. At the last panel we got to see the eyes and I checked, it was exactly like jurion. In that chapter we also saw how jealous jurion was when he saw Jiwoo and jiyoung walking away.
Correction, It was chapter 327 and jiyoung was spending more time with Jiwoo and not with Jurion.
Now all I want is for that Jurion getting his ass handed to him. (For people who don't remember, jurion is the one who probably gave Duke the pill since he is the one who wanted to help duke with the assassination of Jiwoo. All this because the dude can't accept that ji young’s affection is towards Jiwoo)
(Also schnauder looked upset slightly but maybe that's just my eyes.) Anyways Duke is dead finally.. I don't have any sympathy for him since he was too far gone.. I mean he betrayed the WAA arc kids (One of them even died, Asher lost his arm ╥﹏╥) he was always causing too much issues for Jiwoo so it's good..
To be honest, I really badly hope that author don’t do this to sucheon… I don't want him to go all villain.. Maybe a healthy rivalry.. Please