The study of evolution gives a mechanism through which a sense of morality is 'hardwired' into us for its adaptive benefits. Or, less teleologically, the study of our own brains can provide evidence for us as humans just not liking certain things.
Additionally, a technique like group simulation could show that allowing murder is against the average individual's interest.
I'm not claiming I come to my beliefs through deliberate scientific reasoning, but I do think that science has important things to say about most things.