From the book, Wit and Wisdom of Good Pope John, is this story,
During a visit to the Regina Coeli prison in Rome, the Pope requested that the inmates be allowed to leave their cells so that he might address them in the main courtyard of the prison. In the course of this speech he did not hesitate to recall that one of his cousins had once been arrested for poaching and had served a stretch in jail
The Pope exressed pleasure at this opportunity to visit these incarcerated thieves, murderers, seducers. "I have come," he said, "you have seen me. I have looked into your eyes, I have placed my heart alongside your hearts. Be assured that this meeting will remain deeply engraved in my heart."
Among the prisoners who were allowed to approach the Pope, there were two murderers. One of them, after kissing the Pontiff's ring, looked up at him with deep sadness on his face. "Are those words of hope you have given us meant for such a great sinner as I am?"
In response the Pope bent over the convict and embraced him.
Another important note that shows how important prison ministry was to Pope John XXIII is that he only used two missals in celebrating his Mass: one had been presented to him by the inmates of Melun; the other was a gift from the convicts of Regina Coeli.