Life means a Life sentence, as in you are never free. That does not mean you spend the rest of your life inside a prison.

This murderer will still be under supervision until they die, will have particular restrictions about how they live their life, and will be recalled to a prison for almost any minor offence. However the parole board will have made a decision that they are unlikely to offend again and so it is better for society, the taxpayer (and the individual) to allow them to live outside of the prison walls,