2nd premise: Muhammad was the final prophet, following the likes of Abraham, Moses, Isaiah and Jesus. True Islamic followers must also observe the teachings of these prophets. You can't just pick and choose which prophets you want to follow. Moses was given the laws about murder, stealing, and bearing false witness against one's neighbors. Jesus told us to love our neighbors as ourselves, love your enemies and to do good to those that hate you. He also said, "blessed are the peacemakers".
Jesus also refers to himself as the Son of God, but Islam does not. So how do they deal with that? Do they alter His teachings somehow? (Myself, I don't know.) This might be taking us further into what true Islam means than you may have wanted to go.
Wade.