By no means do I believe in an algebraic approach to viewing sins, however, if you lied to save his life, not only would you have saved his life, but you would have prevented the murderer from committing a sin, so by not telling the truth, you performed two acts of "goodness". Besides, most of the lies in the bible that are condemned are attempts to deceive that were for personal benefit. These attempts to deceive that you are discussing would actually be committed with the wellbeing of others in mind. Of course, even with the best intentions, nobody should commit a sin that affects anything else negatively. But I do not believe that this type of lie is wrong.