Donald Trump may still be defending his pal Vladimir Putin from charges that he had Russian dissident Alexander Litvinenko killed in London (“Who knows who did it?” The Donald says), but pretty much the rest of the world has accepted the finding of a British inquiry which determined that the Russian president was “probably” responsible for this crime.

The question is what to do about it?

So far the answer is “not much.” The British government is offering various excuses for why the relationship with Russia is far too important to compromise — as if there is any way to deal civilly with a ruthless and rapacious tyrant like Putin. Obviously, no one is going to start World War III over the Litvinenko murder, but it is vitally important in this case — as it is in the case of Russian aggression against Georgia and Ukraine — to uphold some semblance of international norms. Countries can’t simply go around killing critics abroad and expect to get away with.

And, before Trump interjects in defense of Putin (“We kill a lot of people, too”), it is important to point out a huge difference between the murder of Litvinenko and the killings of terrorists carried out by American drones: The U.S. government is killing people who are plotting terrorist attacks against us and our allies; the Russian government killed a peaceful man who was trying to document Putin’s crimes.

Bill Browder, a financier who was expropriated and expelled by Putin, makes a good suggestion — add the names of those responsible for Litvinenko’s death to the Magnitsky List. Sergei Magnitsky was Browder’s lawyer in a case against the Russian government, who was arrested, tortured, and killed in prison by Putin’s goons. The Magnitsky Act, passed by Congress in 2012, imposes asset freezes and U.S. visa sanctions on those linked to Magnitsky’s murder.

Putin was outraged and made all sorts of blood-curdling threats about what Russia would do in response, but it turns out that, like Trump, he is a foul-mouthed bully who backs down when confronted. In the end, Russia didn’t retaliate beyond ending American adoptions of Russian babies, which is inflicting punishment on Russian orphans. Now the U.S. government could easily expand the list to cover Litvinenko’s killers. So could the British government. And without undue fear of retaliation.

Putin is uniquely vulnerable to this kind of pressure. As a top U.S. Treasury official just noted, Putin is at the center of a web of corruption that has greatly enriched him. In 2007, the CIA estimated Putin’s wealth at $40 billion. Imagine what it is today. He may very well be the wealthiest man in the world.

Where does Putin stash his cash and other assets? Some if it is in Russia, but a lot of it probably is not. Russian oligarchs have parked a lot of their money in offshore banking havens such as Cyprus, Switzerland, and London, where they bought a lot of real estate. I bet MI6, the CIA, and other Western intelligence agencies have an idea of where Putin’s money is sitting, notwithstanding elaborate cutouts and subterfuges. (If they don’t, it constitutes intelligence malpractice.) And if you know where the money is, it is possible to hurt Putin in his pocketbook — something that will be a lot more painful to him than more general sanctions on Russia which don’t affect his luxurious lifestyle.

President Obama, Prime Minister Cameron, and other leaders should act quickly to make Putin pay a price for his transgressions — even at the risk of earning the ire of Russia’s president and his No. 1 fan, Donald J. Trump.