Some say that the mother's love is infinite, so that this one might be possible.
The guy was a monster and had drunk a lot once more. He lived with his mum despite his age, 40 years old.
The poor old woman had already told him that she could not cope with his drinking habits anymore, that she was getting tired of cleaning the house, paying the bills, and others.
He arrived in that state and came by car.
The poor mother was in the front yard collecting his clothes.
He did not see her or could not stop the car in time, so that he ran into her. After he heard her yelling, he thought that the yells were coming from the back and he had simply put her against the wall, so that he went forward with the car finishing to kill her.
Being as drunk as he could be, he thought that she was sitting on her chair, as usual, so that he went in and slept until the next day, lunch time.
When he finally recovered part of his senses, he found the mother squashed under his car. He still heard her voice from beyond, however: I love you, my son.