So it's really difficult to think of a practical example of this, but imagine there were some scenario in which, G-d forbid, you needed to kill a non-guilty party in self-defense. If one were in this scenario, what should one do, according to Jewish law?

On one hand, there are a whole slew of sources seeming to say that we don't give up our own life to save another's. On the other, there is the idea that one should give up his life rather than commit murder.

May you/should you/must you kill him? Please bring canonical sources.