Sinon asks Kirito how he was able to overcome the memories of the deaths he committed. Kirito explains that he didn't overcome them, but accepted the gravity of the lives he took. It was the least he could do to atone.
Afterwards, they discuss just who, and what, "Death Gun" is. Even though "Death Gun" showed off his ability to kill others in the real world with a pistol, he attacked Kirito with his primary weapon, a sniper rifle. Based on this, Kirito deduced that "Death Gun" had to make some kind of preparation before killing his intended victims. Also, players registering for the "Bullet of Bullets" tournament could input their real-world information to be eligible for prizes. "Death Gun" likely used his optical camouflage to spy on his targets and gather their information.
Kirito realizes that "Death Gun" is not just one player, but multiple conspirators working under a shared identity: one played the game as Sterben while others would infiltrate the homes of the intended targets to kill them in the real world, most likely with a drug that induces heart failure. The conspirators in the real world would watch a livestream of Sterben and wait for a signal from him, a "sign of the cross" gesture, before making the lethal injection.
It would be easy enough to infiltrate the victim's homes if they lived alone and had outdated electronic locks on their doors. Sinon lived alone and had no chain on her door. She realizes that a killer could be in her apartment this instant, ready to kill her. This realization drives her into a panic attack that nearly forces her Amusphere to log her out, but Kirito manages to calm her down: as long as Sterben doesn't shoot her with his pistol, she would be safe.
In ALO, Kikuoka logs in under the handle of Chrysheight. When Yui and Chrysheight explain the situation involving "Death Gun", Asuna demands to know where Kirito is in the real world.
Back in GGO, Kirito and Sinon form a plan of attack: Kirito would draw out Sterben while Sinon attacked with her rifle. With cameras now following them, it becomes clear that there are few players left in the tournament. A confrontation is imminent.