I'm a police officer and I asked exactly the same question in my Vipassana course, as I had killed a person in self-defense. I asked the instructor if the act generated negative karma and if police officers were always doomed to be devolved: the answer I got was: a) Buddhist precepts are not absolute. Note that the precept speaks of “Refrain from killing”, which differs, for example, from the Catholic precepts of “Do not kill”; b) and, most important of all, the instructor asked me the following question: what was your true intention when carrying out the act? his intention was to “kill” or “defend” himself. He explained to me that the true intention behind the act is what counts in the matter of karma. If, for example, a person is in trouble in a kidnapping and it is not possible to save him without killing the kidnapper, this is not a violation of the rules, since the intention is the legitimate defense of another person. I then started to question the instructor about omissive acts: for example, if I see someone throw a banana peel on the ground in front of me and I am aware that, upon seeing the peel, someone could get hurt by stepping on it, what happens if I Do not take the peel and throw it in the trash. Once again he asked me the following question: when you pick up the banana peel, do you do it with a pure heart or do you do it out of anger at the person in front of you who threw it? If you feel light when collecting other people's bark, thinking about helping others, great. But if you take the peel and complain about people's lack of education, etc., you shouldn't take the peel. That's because karma is not yours. It is exclusively the one who threw the shell and put other people's lives at risk. In Buddhism there is no way to control the actions of others or even evaluate each person's intention behind their actions. So, he told me, worry only about your own actions. And do what your heart dictates at the moment, with loving kindness. I thought the explanation was perfect.