Paul is never once recorded in the Bible as apologizing or repenting for his persecution of the church.
The closest thing we have from Paul is his acknowledgement he is less than the least of all saints,(Ephesians 3:8.) and the least of the apostles.(1st Corinthians 15:9.)
It should go without saying that whoever persecutes the church and does not show repentance of that fact should be questioned. Would you trust your child's murderer around your other children, even twenty years after the fact, if he did not repent?
Value of this Evidence
This is not indefensible evidence of Paul being a false apostle. Only a certain number of letters from Paul found their way into the canon of the Bible. Perhaps Paul wrote he repented of his evil acts in an unrecorded letter.