Is there a precedent in Jewish law for a case where someone is either forced to kill one person in order to save a group of people?
A precedent is found in Shulchan Aruch 157:1, in the glosses of Rabbi Moses Isserles (popularly known by the acronym, RM”A): “If someone says to Jews, ‘Give us one of you to kill, and if not, we will kill all of you’ – do not give them anyone, unless they specify the individual they want. Even then, there are those who forbid it unless the one they specify is actually deserving of death.” So even handing one innocent person over is not allowed, and certainly it would be forbidden for us to kill the person ourselves.
Best wishes,
Michoel Reach