Can ptsd be caused by something happening to someone else. Like if they watched someone else get killed?
Yes. From my Demystifying the DSM-5 post on PTSD:
A trauma is defined as being exposed to actual or threatened death, serious injury, or sexual violence, in one or more of the following ways:
- Directly experiencing it
- Witnessing in person the trauma as it happened to someone else
- Learning that the trauma happened to a close family member or friend. If the person dying or nearly dying is the traumatic event, it has to have been violent or accidental
- The character has been repeatedly and excessively exposed to awful details of traumatic events. This is typically seen in first responders, police officers investigating child abuse, etc.