My area of study was the Celts; I probably shouldn't be talking about the Bronze Age because there's no solid evidence for Celts that far back. Even in the Iron Age, we don't know for sure what they believed or how their belief system(s) worked, because they left no written sources. The earliest written sources that talk about the Celts are Greek, and therefore written by outsiders. So depending on the geographical areas you're looking at, the lack of written sources will definitely hinder any attempts at figuring out what exactly people believed.

I think, however, that it may be fair game to say that Celtic belief systems of the Iron Age probably didn't have a concept of morality that we would necessarily recognise. The dominant concept that comes out of both Classical sources on the Celts and later Christian writings by Celtic peoples (read: the Irish) is honour. So rather than believing that you shouldn't kill because it's an immoral act (a Christian viewpoint), you might have believed that there were situations in which killing was the most honourable action, eg if you had been challenged to single combat, or killing your family to prevent their capture by enemies (this is a subject of Classical sculpture). But it's very hard to know anything for sure, because we just don't have the sources necessary.

I think this question will be difficult to answer for a couple reasons. First, there were quite a few diverse cultures active in the Bronze Age, so you might want to narrow your answer down to a specific region. Some of the big ones I'm familiar with are the Minoan and Mycenaean civilizations in Greece, the Mesopotamian cities (Babylon, Ur, Sumer, etc), and the Egyptian dynasties. However despite having many rich cultures, writing was still in it's infancy so we don't have as much written record, which is mostly where you would find a culture's moral beliefs and enforcement.