The Mystery I Loved

A murder occurs in an apartment. The victim is a famous detective author. A card left in the scene shows that the somebody who called himself as character of the author's detective novel took the life of the author. Two suspects were identified: the guard of mansion who likes to drink despite author telling him not to, and the editor of the publishing company who claimed that the author was alive when he left the room. After finding evidence through sushi, the culprit was revealed to have done it out of love for the author's mystery