It's worth considering R v Dudley and Stephens (http://en.wikipedia.org/wiki/R_v_Dudley_and_Stephens) - a real world case - and The Case of the Speluncean Explorers (http://en.wikipedia.org/wiki/The_Case_of_the_Speluncean_Explorers) - a fictional case written to illustrate the law - concerning stranded people killing and eating one of their number to stave off starvation. In the former there seems to have been swings in public opinion, but much of the time, public opinions seems to have been pretty sympathetic. Likewise in the latter case, most or all of the fictional judges are sympathetic - however, this doesn't necessarily alter their interpretation of the law.

That said, the case is more akin to B shooting A, than C shooting A.