I revisited this discussion because Chaim mentioned Yigal Amir in the newest video. I want to give the specific sources of my arguments for my own reference and for the benefit of others:
"If a person committed homicide because another person was threatening his life (or limb or severe torture), this killer has committed an offence and is a murderer and will be punished by Heaven. However, a court of law does not have permission to punish him, because he was severely pressured" (the Divine Code by Rabbi Weiner, Second Edition, p 403, citing Rambam, Laws of Kings 10:2).
"It is not permissible to save someone by killing his pursuer unless this is the only way to save the victim. If it is possible for one to save the victim without killing the pursuer - for example, by appeasing him or confusing him with words, or by wounding him, as by cutting off his hand or foot - and instead he killed the pursuer, this considered murder with liability to capital punishment" (the same, p 407, citing Rambam, Laws of Kings 9:4).
"Whoever bears the sin of murder without proper repentance is considered an absolutely wicked person (and he has no portion in the World to Come), and not even the sum total of all the Divine service and good deeds that he accomplishes in his life can outweigh the gravity of this sin" (the same, p 462-463, citing Proverbs 28:17, Rambam, Laws of Murderers ch. 4 and Laws of Repentance 3:6).
"Some topics apply to both Jews and Gentiles, but this book only comes to teach the Noahide Code. Thus, Jews should not use this text to determine their own obligations, which are more restrictive and numerous" (the Divine Code by Rabbi Moshe Weiner, Ask Noah International, 2018, p 22).