If I had control of the movie, the mother and son should've had some form of closure as they are forced to fight for their lives. Build the tension with the mother and son fighting. But as the killer begins to reveal himself; they are forced to also overcome the pain the two brought. Perhaps the mother blaming the son for her husband's death. OR the son living with guilt of this situation. Or perhaps returning the blame on the motehr which forced this divide in their relationsip.
A movie like this fairs better when the two protagonists manage to bond over a dangerous tragedy that makes them face their demons about one another; and value the bond of their family. If the killer managed to horribly injure one of the protagonists. A good moment that could've occured is some attack that occurs after the mother and son fight once more. The killer is there but whatever fight transpired put them on a single strand keeping the family together. Here, the son sees that same expression of fearful confusion on his mother's face that his father had before dying.. and he goes back to save her; despite having some great desires leaving.
This movie was garbage in the sense that it just built up to two people being killed and the murderer getting away with it. Yes, the premise is that being in the wrong place at the wrong time. At the same time; the family had all this tension built up and could've made an impactful show of human relationships in the face of death itself. The bond between mother and child still there.