The case in question is episodes 5-6 of Sword Art Online

Let’s not get into a whole discussion about the rest of Sword Art Online, alright? I liked a lot of the episodes in the first part of the story. This murder in a safe zone case of course stuck out. And thanks to a comment on the last installment of this article series, I realized I had neglected this mystery for No Case Too Small.
Since Sword Art Online takes place inside an MMO there are certain structures and rules set-up by the game that can’t be broken by just simply wanting to do so. One of those is safe zones which prevent “player-killing.” So when Asuna and Kirito stumble upon what appears to be a murder in progress, everyone is understandable alarmed.

Asuna and Kirito are on the case after talking with a witness and former guildmate of the victim. The guild had broken up after the death of one of their members, Griselda, and suspicions about the rare tem she was going to sell before her death. Perhaps the victim’s husband is taking revenge? A ghost perhaps?
Then a second murder happens right before their eyes.

