What term describes a situation where an armed person is killing or attempting to kill in public?

The term that best describes a situation where an armed person is killing or attempting to kill in public is "active violence." This term emphasizes the immediate and ongoing nature of the violent act, specifically indicating that the threat to life is current and requires urgent response measures. Active violence situations generally involve the use of weapons and the intent to harm multiple individuals, creating a chaotic and dangerous environment.

In contrast, the other terms present distinctions that may not capture the intensity or immediacy of the violence. For instance, "active threat" can refer to any ongoing situation where there is a potential for violence, not necessarily the act of killing itself. "Active aggression" might imply hostility or violent behavior but does not highlight the lethal aspect or urgency of the situation. "Active disturbance" is more vague and could relate to various forms of disruptive behavior, which do not clearly denote the presence of armed violence or the intent to kill. Therefore, "active violence" is the term that most accurately conveys the severity and nature of the incident as described.