What happened to people who committed crimes (such as killing) in SAO?
From the end of the ALO arc in the novel, where Kirito thinks about his school and the policy to avoid using in-game names:


  In this special «school», the students were players who had been in middle or high school before the SAO incident. Those orange players with a serious history of murder were undergoing more than one year of counseling that included treatment and observation. People like me who attacked others for self-defense, were inquired without leaving a criminal record like theft or blackmail.