killing a sith lord

back before hutt cartel expansion i had a imperial agent manage to kill darth jadus in chapter 1, chapter 2 i was brainwashed by sis cause the dark counsel feared me for killing one of there own so sis took advantage for the duration of the mind contol watcher x helped me break free as i killed each sis agent during the missions, then in chapter 3 i met a rogue agent that wasn't aligned with any faction i killed him at the end of chapter 3 taking the cube and declaring myself that i am imperial inteligence.  since then i had deleted that character during the revan expansion, since getting back into old republic i cant find the option to kill him again along with reading about people who say he cant be killed in chapter 1 even though he can be killed in chapter 1 is rather dissapointing in todays player base that no one has tried i respectfully ask is there anyone who even remembers that option to kill him or if swor manages to read this did you remove the option and why   thank you for your time