A mass murderer who repents and asks God to forgive him is forgiven and becomes a Christian, a follower of Christ. He is no longer considered a mass murderer by God, but a son.
1 Corinthians 6:9-11 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality, nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God.
And such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.
Forgiven is forgiven.
For some reason that is unfathomable, Catholics have a really hard time understanding what forgiveness is all about.
It's NOT about working off a debt owed, or paying for our sins.
It means forgiven. Freely. Without cost or obligation.
If there's any strings attached, it's not forgiveness. It's a gift given us by God.