I came up with good links for you to start with.
- The Homicide Witness and Victimization
- The Effects of Witnessing the Violent Death of a Loved One
- Experience Project: I Was Witness to a Murder
- Witnessing Violence and Death
- Your Child: Childhood Trauma and its Effects
- Fact Sheet: Witnessing Violence
- Children Who Witness Parental Murder
What I’d like you to do is to research this matter as much as you can in order to portray it accurately. Witnesses of crime often have to deal with a big amount of trauma and fear in real life, and the least you can do is try to depict it as best as you can.
Best of luck.
Someone just asked about childhood trauma. Another effect can be amnesia. Sometimes a person just forgets a stressful/traumatic event for what could be years until something triggers it. It sets in within a few days of the event. It’s a real thing and normally (upon return of the memory) the person just ignores it’s occurrence and depression can follow. - catcher-in-the-sky