And it came to pass in those days, when Moses was grown, that he went out unto his brethren, and looked on their burdens: and he spied an Egyptian smiting an Hebrew, one of his brethren. And he looked this way and that way, and when he saw that there was no man, he slew the Egyptian, and hid him in the sand. Exodus 2:11-12
"Verse 12 states that Moses killed the Egyptian only when “seeing no one.” According to one interpretation, it is not to be understood that Moses was afraid or had a bad conscience. Instead, the text should be read in light of Isaiah 59:15-16, where exactly the same Hebrew expression appears, “The Lord saw it, and it displeased him that there was no justice. He saw that there was no one, and was appalled that there was no one to intervene; so his own arm brought him victory.”
Moses was not indifferent; he intervened when he saw that no one cared for justice. Moses realized the depth of the suffering of his people, not only from their outward oppression but also their inner distress. While this interpretation may not do justice to the context, it is nevertheless thought-provoking and instructive."
(Larsson, Göran., Bound For Freedom, Hendrickson Publishers, Inc. Peabody, Massachusetts, 1999, pg 24)