It's a pretty straightforward question - how involved your answer is depends on you. Is the threat of imprisonment (or the death penalty in some places) the only thing preventing you from killing someone? Or are moral reasons enough to keep you in line?
Imagine also that there would be no other repercussions such as revenge attacks from relatives of the victim, etc. So the decision is entirely your own, with no consequences other than the direct result of the act, and any effect it may have on your conscience.
In other words, if you could get away with it completely, would you commit murder? Or is it something you would never wish to do, or couldn't bring yourself to do if you wanted to?