Everyone knows Ming Yi has his shovel, and that Shi Qingxuan and Ming Yi are rarely apart. But Steven was the one killed with the shovel.

... I think he worked with someone. Potentially Steven was his victim, and Luca was his accomplice's victim. They met up at the end, and that's when Vlad was killed. Same way as Luca was, and the croissant flakes in his mouth show he was in the same place Luca had been at some point.