There is nothing that can “justify” murder, there are only things that can *explain* it. Cause-and-effect operates outside of morality. Which is not to say that murder (or any human action) can be boiled down to a single cause but rather that a confluence of circumstances can be understood to have a certain potential to lead to a specific outcome, not unlike the way we understand the physical sciences. For example, different plants grow in different areas of the earth, they require a specific set of ecological circumstances in order to thrive, and changes to the environment consequently change the way plants grow, evolve, or die.
Human behavior is of course more complex, but I believe it still operates under the same basic laws of nature. By extension, I would argue that when you live in society dominated by a tiny minority of wealthy individuals who use murder, torture, exploitation, oppression, deception, etc. as a way to maintain their rule, you can expect to reap all sorts of unhealthy outcomes, including a police force that murders with impunity and individuals who see no other recourse than to murder back.
I do not believe we should seek to justify either side of this cycle of violence; rather, we should seek to expose the underlying causes of violence and move forward with the project of transforming this society into one that is capable of producing good rather than evil. Your individual morality does not change the inherent immorality upon which our current society is based. Only collective action can do that.