Witness

A person who has seen the event happening, was present at the time of the crash but not directly involved in the action (1). Posttraumatic Stress Disorder (PTSD) can occur not only in individuals directly experiencing life-threatening situations but also in witnesses to traumatic events—such as a serious traffic accident, a catastrophe, or violence. The DSM-5-TR explicitly recognizes this possibility in its diagnostic criteria. Witnessing such experiences meets criterion A2 for PTSD (2).

Source: (1) https://dictionary.cambridge.org/dictionary/english/witness