The issue is not whether a murder can become a Christian, but can a murder be forgiven. Love is both positive and negative. We know that we have passed from death to life, because we love our brothers. Anyone who does not love remains in death. Anyone who hates his brother is a murderer, and you know that no murderer has eternal life in him.
Christian love is personal and active.
The parable of the good Samaritan is a story about loving our neighbor. Jesus focused on the need of one man. He used a priest and Levite in his parable to illuminate his answer. The priest and the Levite should have been setting the example for others. Jesus used the Samaritan whom the Jews hated to teach the Jews how to be a neighbor.