SERGEI MAGNITSKY's legacy continues to expand far beyond what he might have imagined. Magnitsky died at the age of 37 in a Moscow jail cell in 2009 after uncovering a mammoth fraud in which Russian officials awarded themselves a $230 million tax break. The United States later passed legislation bearing his name providing for sanctions against those who are serious human rights abusers. Britain has done the same, and recently, so did Canada. The Magnitsky acts are a protest against venality and a bulwark against impunity.

Magnitsky's death was cruel; Russian officials failed to give him proper medical treatment. His employer was William Browder, once the largest portfolio investor in Russia. Mr. Browder became a tireless advocate for sanctions against the officials who caused the death and others like them.

This principled activism angered Russian President Vladimir Putin and his wealthy cronies in Moscow, whose travel and financial freedoms were cramped by the sanctions. Last year, in the middle of the U.S. presidential campaign, a lawyer for some wealthy Russians visited Trump Tower with a wish list that included easing the Magnitsky sanctions. Just last week, Mr. Putin, at the Valdai Discussion Club in Sochi, lashed out at Mr. Browder, accusing him of being involved in "crime, deception and theft." Russian officials have repeatedly tried to prosecute Mr. Browder on various trumped-up pretexts, including recently the outrageous charge that he, and not the prison officials, caused Magnitsky's death.

Now Mr. Putin is at it again. After Canada passed its version of the Magnitsky act this month, Russia on Oct. 17 filed a notice against Mr. Browder with Interpol, the international network of police forces. Unlike a "red notice" seeking arrest of a wanted person, which is checked to avoid its use for political purposes, Russia unilaterally filed a less formal "diffusion" notice, intended to request arrest or more information about a person or investigation. The diffusion notice went out to all 192 nations who are Interpol members, and Mr. Browder, who is a British citizen, says it had the effect of disabling, temporarily, his ability to enter the United States without a visa.

Interpol has been attempting to halt abuse of the red-notice system, as the nongovernmental organization Fair Trials has urged. The reform effort needs to run deeper and guard against politicization of the Interpol diffusion notices, too. The United States should also be on guard against diffusion notices intended to silence dissent. It is wrong to allow Mr. Putin's vengeful rants to be translated into action. Magnitsky's legacy is that violations of human rights will not be tolerated, and those who speak out will not be silenced.