There is a well-known story of St. Therese of Lisieux and a criminal, Pranzini.
As a youth of 14 years, Therese had prayed for this "notorious" murderer, who was sentenced to death. Tenacious and unrepentant -- moments before his execution, he asked for a crucifix, which he took and kissed. Therese took this as a sign she had prayed for.
For more background, see:
https://www.catholicworldreport.com/2017/10/01/the-killer-and-the-saint-pranzini-and-therese/
There is, however, a bit more to the story.
Evidently this man, in spite of his dreadful crimes and wretched behavior, held at least a small devotion in his heart for the Blessed Virgin. It is said that on a couple of occasions, when passing by the local cathedral, he had stopped in to pay a short visit to her.
While not denying the value or efficacy of Therese's prayers, it was perhaps the intercession of the most Blessed Virgin at work in this instance also. Our Lady looked with love upon this pitiful soul: she would not allow one of her wayward children to perish for all eternity. And she helped obtain the miracle.
This account helps illustrate an important point. At many times and in many events in our life (often without our knowledge or understanding), Mary is there at work behind-the-scenes. Praying, helping, interceding for us... In ways that only she can.
