Bullies are repeat offenders. The pattern of abuse is evident to all HR departments. There is some guilt implied because of this pattern. Take into account the perpetrator's record. Incidents are not unique and isolated.
Risk management has data about litigation or settlement costs associated with repeat offenders.
Treat seriously stress claims and reports of psychological injury. They are as counterproductive as physical injuries and last longer. Stop blaming victims. Bullying is a safety and health issue. Do not compel the injured target to participate in a dispute resolution process in which she or he faces directly the perpetrator.