No. We are talking about divine justice. That you believe Paul was in the right to contribute to the murder of Stephen is a bit off.No, what he did was legal as he was given authority. He brought them to the authorities. Not sure why that needs explaining.
irrelevant
Abortion is legal. Doctors have the authority to perform abortions. That does not mean it is less than murder.
Why assign your idea of secular justice to God?
To address your question:
Say an 18 year old man kills another and gets away with it. Years go by. God works in the life of this man. The man grows, changes, marries, has children and then grand children. He becomes a pillar of the community. As a great grand father he is finally caught and tried for murder.
Your justice is the man should face the death penalty. That would be secular justice. But is it justice? That is debatable. Yet you assign to God your philosophy of justice without defending your decision. Scripture tells us that God forgives based on repentance (true repentance). This is above your idea of justice.