What should i do in the following scenario?

Pls help me with this decision 1)My bully's father made my mother uncomfortable 2)Now i do not know if it is only standing close to her and talking or if he did something worse(like touch her inapproproiately.) I have to ask her to know the details.I only know that he made my mother uncomfortable. 3)Now it has been 1 year since the incident. So considering that 1 year has passed,my question is:- 1)Should i enquire from my mother about what happened and then pursue it legally 2)or should i just let it go and move on?