God does not allow any crime to go unpunished. In human terms, a crime may evade human systems of justice, but they do not evade God.
If we repent of sin, God will forgive us in our relationship with Him and in Eternity. This gives us a fresh start each day where God is concerned, which is liberating, empowering us to press forward. But, we still must do restitutions—work to clean up whatever mess we made in the natural universe during our life on Earth. It wouldn’t be loving toward others if we didn’t clean up the mess we repented of making.
More importantly, time wasted sinning is time better spent building up value that matters in the eyes of Heaven—things that God congratulates rather than forgives. If one’s life only surmounts to forgiven sin then one would enter Eternity with nothing.
These balance out in the end, including the vindictive need for punitive acts of justice and revenge. Someone who hurt you may repent, clean up his life, and start contributing to make life valuable for people—preventing others from the same destructive path. However and whenever God punishes others, we always find it just and beg for His mercy on them.
But, for the unrepentant—for the people who care nothing for others or for justice, who commit heinous crimes against humanity—their day in court with the Lord God Most High is indeed coming.
God punished Cain for murdering his brother, a curse and guilty conscience that followed him the rest of his life. The world, full of wickedness and murder, was drowned in the flood of Noah’s day. Babylon’s economy never regained its investment for the Tower unfinished. Egypt enslaved Israel and did not recover the bruises of a wrathful God. The defiant generation of Israel died in the desert. Satanic human-sacrificing cultists in Canaan were rightly slaughtered by Joshua’s army. Enemies of the judges suffered humiliating defeat as did Saul and his family.
When God wielded evil nations to punish Israel for sin, they too were decimated—Assyria, Babylon, Persia, Greece, and Rome.
In the end, Revelation predicts indescribable vengeance on unimaginable wickedness because nothing escapes God’s vindication.