“Each state is expected to aid and enforce the law of nations, as part of the common law, by inflicting an adequate punishment upon the offenses against that universal law.” William Blackstone, Commentaries on the Law of England (1765)

Israel’s targeted killing of Hamas leader Marwan Issa in mid-March raises tactical and legal questions. Though it is unclear that such tactics can diminish tangible terror threats to Israel, there is also no reason to rule out their permissibility under international law. In the final analysis, such permissibility derives from the world legal system’s continuously anarchic structure and from the corresponding right of all nation-states states to protect their citizens from willful slaughter.

There are many clarifying details. By definition, world legal authority remains a fundamentally “self-help,” or vigilante system of justice. It is amid this perpetual global anarchy that every anti-terror government must systematically assess its strategic and tactical options. The victim of this necessary act (a targeted air attack) was a key Hamas planner of the October 7, 2024, assault on Israeli civilians, a murderous terror assault that combined the mass killing of noncombatants with the orchestrated rape of Israeli civilians.

Hamas, like Hezbollah, draws tangible support from Iran. A principal risk of leaving this insidious symbiosis unchallenged would be a direct Iranian attack on Israel that escalates incrementally into unconventional belligerency. Eventually, even if Iran were to remain non-nuclear, an intra-crisis search for “escalation dominance” by Israel and Iran could produce unprecedented nuclear conflict. This sui generis result could be produced suddenly, as a “bolt-from-the-blue,” or in variously hard to decipher increments. Initially, it could “present” as an Iranian use of radiation dispersal weapons (nuclear radiation rather than nuclear explosives), or as a conventional attack on Israel’s nuclear reactor at Dimona.

Under international law, which is binding upon all sovereign states, terrorism represents a crime that should be prevented and must be punished. As was learned originally from Roman law and Jewish law (Torah), a universal rule exists. This “peremptory” rule affirms the core principle of “No crime without a punishment,” or Nullum crimen sine poena. It can be discovered, among other sources, at the London Charter of August 8, 1945. This is the founding document of the post-war Nuremberg Tribunal.

In formal jurisprudence, terrorists are known as hostes humani generis, or “common enemies of humankind.” While the world legal system allows or even encourages certain insurgencies in matters of “self-determination,” there is nothing about these matters that can ever justify deliberate attacks on civilians. In this connection, it is important to remember that an integral part of all criminal law is the underlying presence of mens rea, or “criminal intent.”

On this point, there can be no reasonable comparison of Marwan Issa’s deliberate mass murder of Israeli noncombatants, and the unintended civilian harms now being suffered in Gaza. As a matter of law, responsibility for such ongoing harms falls entirely upon the “perfidious” behavior (i.e., “human shields”) of Hamas and Iran, and not on Israeli forces acting on behalf of legitimate self-defense.

Under the law of war, even where an insurgent use of force has supportable “just cause,” it must still fight with “just means.” Accordingly, the vapid phrase “One man’s terrorist is another’s freedom fighter,” is never more than an empty witticism.

There is more. Ordinarily, assassination, like terrorism, is a crime under international law. Under certain conditions, however, the targeted killing of terrorist leaders can represent a life-saving and heroic example of indispensable law-enforcement. In a more perfect world legal system, perhaps, there could be no defensible justification for any violent self-help expressions of international justice. But this is not yet such a world.

In our self-defense oriented world legal order, the only state alternative to launching precise targeting actions against terrorists would be to allow incessantly escalating terror-violence against the innocent. Among pertinent clarifications, this is because terror-organizations like Hamas and terror-mentoring states like Iran harbor undisguised contempt for all ordinary legal expectations of criminal extradition. The formal term for this ignored expectation is “extradite or prosecute;” or aut dedere, aut judicare.

At first glance, to accept the targeted killings of terrorist leaders as law-enforcing remediation would seem to disregard the usual obligations of “due process.” Still, international relations are not overseen by the same civil protections offered by individual national governments, and terrorist leaders like Marwan Issa undertake barbarous attacks on men, women, and children with undisguised enthusiasm.

In the future, if Hamas and related terrorist criminals are effectively held immune by civilized states, indiscriminate attacks could exploit chemical, biological, or even nuclear elements. For the moment, a nuclear option would be limited to “only” a “dirty bomb” (radiation dispersal weapons), but this could change. To be sure, in the foreseeable future, Iran could fashion and deploy an authentic “chain-reaction” nuclear explosive.

There is more. The willfully indiscriminate nature of jihadist terrorist operations (not just Hamas) is well documented. Such intentional blurring of the lines between lawful and unlawful targets is rooted in certain generic principles of “holy war.” Several years ago, an oft-repeated remark by Sheikh Omar Bakri Muhammad, then a prominent Muslim cleric in London, explained core doctrinal linkages between Islamic terror and “holy war:”

Said the Sheikh, “We don’t make a distinction between civilians and non-civilians, innocents and non-innocents. Only between Muslims and unbelievers. And the life of an unbeliever (a Jew or Christian) has no value. It has no sanctity.”

International law is not a suicide pact, especially when an adversary remains indifferent to its unassailable claims.

As was learned yet again on October 7, 2023, jihadist attackers add gratuitously barbarous effects to their corrosive primal ideologies. At “bottom line,” these are belief systems that gleefully embrace the sacrificial slaughter of “unbelievers.” To wit, for Hamas and related terror groups, “military objectives” have “normally” included elementary schools, bomb shelters, ice-cream parlors, civilian bus stops, and elderly pedestrians. In law, these perpetrators ought never to be called “militants.” Whatever their alleged cause, they are criminals of the irredeemably worst sort.

There is a related point. Though jihadists may call themselves “martyrs,” the personal death such terrorists seem anxious to suffer is presumptively just a transient inconvenience on the path to “paradise” and immortality. As this path is “glorious,” these jihadists are not “merely” aspiring mass murderers. They are also consummate cowards.

Hamas, Hezbollah, Islamic Jihad, and other terror groups remain dedicated to the idea that any peace agreement with Israel must represent an intolerable abomination to Islam. Facing these implacable enemies within a self-help system of international law, Israel deserves the self-defending right to target refractory terrorist leaders. Determining whether such self-help remedies are also militarily sound raises another question altogether.

In the final analysis, what is most noteworthy about the targeted killing of terrorist leaders is not its permissibility in law, but the widespread global unwillingness to endorse or even acknowledge this critical right.

In current jurisprudence, an ancient principle still holds true: Ubi cessat remedium ordinarium, ibi decurritur ad extraordinarium — “Where the ordinary remedy fails, recourse must be had to an extraordinary one.”

Under international law, every state maintains the inherent right and corollary obligation to protect its citizens from transnational criminal harms. In exceptional circumstances, this dual responsibility can extend to the targeted killing of terrorist leaders. Otherwise, on its face, world law would in fact be a suicide pact.

Targeted killings, subject to applicable legal rules of distinction, proportionality, and military necessity, could sometimes offer the least unwelcome form of national self-protection. In such cases, especially where additional terror-crimes are still in a planning stage, the legal acceptability of violent self-help measures is greater ipso facto. In our continuously anarchic system of international law, this proposition is beyond any logical doubt. The world legal system is designed to protect us all from foreseeable infringements of human rights. Ironically, however, this same decentralized system still has no independent means to meet such a primary obligation.

In the best of all possible worlds, targeted killing could expect no defensible place in law-based counter-terrorism. But we do not yet live in the best of all possible worlds, and the negative aspects of any such action ought never to be evaluated apart from alternative policy outcomes. If Israel had chosen not to target Marwan Issa so as not to injure the sensibilities of “civilized nations” (a phrase codified at article 38 of the Statute of the International Court of Justice), it would have brought extensive injury to many innocent human beings.

Counter-terrorism should always be governed by rational and justice-oriented decision-making processes. If the expected costs of a targeted assassination appear lower than the expected costs of all other plausible self-defense options, such a self-defense operation must emerge as the patently rational choice. However odious it might first appear in vacuo, targeted killing in such circumstances could offer a beleaguered state the least injurious path to security from terrorist criminality.

Inevitably, targeted killings, even of Hamas leaders like Marwan Issa, will elicit righteous indignation from many quarters. For now, however, the philosophic promise of centralized international law remains far from being realized, and continuously beleaguered states such as Israel will need to consider multiple operational choices. In facing such bewildering choices, states would soon discover that all viable alternatives to targeted-killing also include violence, and that these alternatives could plausibly exact a much larger human toll.

Sir William Blackstone’s 18th century Commentaries, the foundation of United States jurisprudence, explain that because international law is an integral part of each individual state’s “common law,” all states are “expected to aid and enforce the law of nations.” This must be accomplished “by inflicting an adequate punishment upon the offenses against that universal law.” Derivatively, by its precisely targeted removal of Hamas terrorist leader Marwan Issa, Israel acted not in violation of the law of nations, but in its indispensable enforcement. Presently, this neglected clarification of global justice should not be undervalued or overlooked.

Louis René Beres was educated at Princeton (Ph.D., 1971) and is the author of many books and scholarly articles dealing with international law, nuclear strategy, nuclear war, and terrorism. In Israel, Professor Beres was Chair of Project Daniel. His twelfth and latest book is titled Surviving Amid Chaos: Israel’s Nuclear Strategy (Rowman & Littlefield, 2016; 2nd ed., 2018). A version of this article was originally published by Israel National News.

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