It could be that someone wronged his mother seriously. Maybe it was an act of injustice like someone cheating her out of her inheritance. So, in order to make things right and seek justice for her, he decided to take revenge.
He might have felt a sense of relief at first. Finally being able to do something about the wrong that was done to his mother could have given him a momentary peace.
Well, without more context, it's hard to say precisely. 'A Mother's Revenge 1993 True Story' might involve a mother who found herself in a situation where she had to take matters into her own hands for revenge. It could be related to personal vendettas, like if someone hurt her child or violated her family's safety in 1993, and she decided to retaliate in some way.
Yes, 'A Mother's Revenge' is based on true events. It shows how a mother's love and the quest for revenge can play out in reality. The story was adapted to bring those real experiences to the screen.