This paper explores whether terrorist violence could be morally justified or excused. It defends the absolute immunity of innocent people against those who might want to sacrifice them for other goals. The defense is based on recognizing people’s stringent natural duty of nonmaleficence, which entails an obligation on moral agents to refrain from intentionally bringing about harm or significant risk of it to the innocent. The paper is divided into two parts. The first part distinguishes between unconditional and conditional critics’ arguments regarding the use of terrorist violence, and between a narrow and a broad definition of terrorism. While unconditional critics accept the narrow definition or one akin to it because they equate terrorism with murder, conditional critics accept the broad definition or one akin to it because they attempt to justify or excuse the use of terrorism based, e.g., on an analogy with a just war approach, consequentialism, moral relativism, supreme emergency or last resort. Exception is taken with the latter arguments since they attempt to justify or excuse morally unjustifiable and inexcusable actions such as the deliberate use of violence against the innocent. The second part explores plausible conditional critics’ reasons for justifying or excusing the 9/11/01 attacks and find them wanting. If the argument works, then, with minor modifications, it could also apply to the 3/11/04 attacks in Madrid, the 7/7/05 attacks in London, and similar attacks elsewhere.