YOU SAID:

I killed the killer who killed my victim's killer

INTO JAPANESE

私は被害者の殺人者を殺した殺人者を殺しました

BACK INTO ENGLISH

I killed the murderer who killed the victim's murderer

INTO JAPANESE

被害者を殺した犯人を殺した

BACK INTO ENGLISH

killed the perpetrator who killed the victim

INTO JAPANESE

被害者を殺した加害者を殺した

BACK INTO ENGLISH

killed the perpetrator who killed the victim