SWORD ART ONLINE SEASON 1 EPISODE 6-ILLUSIONARY AVENGER
Kirito ran after Yuruko´s killer, but didn´t catch him. He insisted that killing in a safe zone is impossible in such a game, and he was sure of it when he was eating sandwiches with Asuna that night.
So, the whole death issue was fake. Kains and Yuruko were not actually murdered. On floor 19, Schmitt went to Griselda´s grave begging her not to kill him since he was given orders by unknown person to steal the item from her. Suddenly, Kains and Yuruko appeared recording all what Schmitt was saying. While the three were talking, a group of three persons attacked Schmitt trying to kill him, but Kirito arrived just at time and saved Schmitt.
Asuna also came and found Grimlock who confessed that he killed his wife Griselda because she was confident and strong enough to play SAO, while he was weak and afraid to die.
Grimlock was left for his guild to deal with him. Asuna and Kirito added each other as friends and and decided to go back for their work before Griselda´s ghost appeared and surprised them.