This article reviews the behavioral, psychological, and situational characteristics of mass murderers through a threat assessment framework. Drawing on case series, investigative findings, and clinical literature, the authors analyze common features including longstanding grievance, social marginalization, leakage, identification with prior attackers, fascination with weapons, and the pursuit of recognition. The paper distinguishes mass murder from other forms of targeted violence while highlighting overlapping warning behaviors and pathways. Attention is given to precipitating stressors, deteriorating coping capacity, last-resort ideation, and observable shifts in behavior prior to attacks. The authors discuss implications for early identification and intervention, with a focus on multidisciplinary team response, information-sharing barriers, and the need for structured models capable of integrating ambiguous or incomplete data.