Brussels   Should Vladimir Putin be studying the conviction of Charles Taylor, the former Liberian president? What about Henry Kissinger?   In April a United Nations–backed special tribunal in The Hague convicted Taylor of “aiding and abetting” the rebels in neighboring Sierra Leone as they committed horrific abuses against civilians. The rebels’ crimes, which included their signature atrocity of cutting off victims’ arms and legs, as well as forcing children to execute their parents, were among the most heartless I have ever investigated.

The verdict marked the first time since the post–World War II Nuremberg trials that a former head of state has been convicted by an international tribunal of war crimes and crimes against humanity. What may be of more lasting significance, however, is that Taylor was not convicted for oppressing his own people—though he did that as well—but for his material support to abusive forces in another country. In that respect, the decision speaks not just to tinpot dictators but to leaders of countries who fight proxy wars by knowingly giving client states or rebel allies the means to commit atrocities.

Following precedents from the Yugoslavia war crimes tribunal, the court—officially called the Special Court for Sierra Leone—said that “aiding and abetting” requires that the accused give “practical assistance, encouragement, or moral support which had a substantial effect on the perpetration of a crime.” The accused must have known that his acts “would assist the commission of the crime by the perpetrator” or be aware “of the substantial likelihood” that they would.

In Taylor’s case, the court found that he knew of the atrocities being committed against civilians by his Sierra Leonean allies “and of their propensity to commit crimes.” Nevertheless, the court said, Taylor continued to ship arms to the rebels and provide them with political and moral support and encouragement. The principle is akin to giving more ammunition to an armed man on a killing spree.

It’s striking that the very same legal reasoning could apply to those in Washington, Moscow or elsewhere who provide military assistance to abusive forces half a world away. Take, for example, the case of former US Secretary of State Henry Kissinger and East Timor. Declassified documents reveal that after the Timorese declaration of independence from Portugal in 1975, Kissinger and President Gerald Ford, fearing that the new country would become a communist outpost, gave Indonesian President Suharto the green light to invade the island in a Jakarta meeting the day before the invasion.

The United States was then supplying Indonesia’s military with 90 percent of its arms, and Kissinger himself described their relationship as that of “donor-client.” As the civilian death toll from the invasion climbed into the tens of thousands and the reports of atrocities mounted, Kissinger ensured that US arms continued to flow to the invading forces despite Congressional strictures. Estimates of those who died from military action, starvation or disease range from 100,000 to 180,000—roughly one-seventh to one-fourth of the entire population of East Timor.

The reasoning might also apply to Russian leaders if it were found that they gave Syrian President Bashar al-Assad the means to massacre his own people. Russia (and before it the Soviet Union) has long supplied Syria with the bulk of its weapons. But even during the latest crackdown, which has become increasingly brutal—including the shelling of Syrian cities with heavy artillery—Russian exports of arms and ammunition have continued. While Russian officials say the weapons are used for defensive purposes, others allege that the shipments include sniper rifles of the kind used by Syrian government forces against protesters.

To be sure, it is hard to imagine a case against a Russian or American leader reaching an international court. Neither country has ratified the statute authorizing the International Criminal Court, and both can veto any Security Council referral to the ICC. Unfortunately, the most powerful, and those whom they protect, still appear to be beyond the reach of the developing architecture of international justice.

Even so, the Taylor decision should give pause not only to leaders who kill their own people but also to those who would arm and support them. As such, it could be a major advance for human rights.