Left, Alexander Litvinenko in a London hospital on Nov. 20, 2006. Right, Litvinenko in London on May 10, 2002. (Left to right: REUTERSAP Photo/Alistair Fuller/Left to right: Handout/Reuters; Alistair Fuller/Associated Press)

BY ALL accounts, Alexander Litvinenko was a bit of a gadfly in London. He once served in the Soviet KGB and later in the Russian Federal Security Service, or FSB, but after blowing the whistle on some shadowy practices, he fled Russia, fearing for his safety, to London, where he became a harsh critic of Russian President Vladimir Putin and of the FSB that Mr. Putin once headed. Mr. Litvinenko dabbled in private security work in London while also serving variously on the payroll of the British security service and the self-exiled oligarch Boris Berezovsky.

Mr. Litvinenko’s criticism of Mr. Putin and the FSB rankled some powerful people. Mr. Litvinenko was warned that his life might be in danger.

At a meeting with two visiting Russians at the Pine Bar in the Millenium Hotel on Nov. 1, 2006, Mr. Litvenenko took a few gulps of cold tea from a pot that had been sitting on the table. The tea was laced with a radioactive isotope, polonium 210. Mr. Litvenenko fell ill that night at home and died of acute radiation syndrome Nov. 23 at University College Hospital in London. In his last statement, he pointed a finger at Mr Putin.

Now Robert Owen, a retired British judge, has carefully and comprehensively documented what can only be called an assassination. Mr. Owen concludes that the two Russians who met Mr. Litvinenko at the bar, Andrei Lugovoi and Dmitry Kovtun, deliberately poisoned him, and also tried to do so earlier, on Oct. 16. Moreover, Mr. Owen found Mr. Lugovoi was acting “under the direction” of the FSB in an operation to kill Mr. Litvinenko — one that was “probably approved” by the director of the FSB and by Mr. Putin.

This raises a serious question for President Obama and other world leaders whose governments do not traffic in contract murder. Should they continue to meet with Mr. Putin as if he is just another head of state? The British report does not prove that Mr. Putin ordered the murder. But at a minimum, he has built a state that operates on the premise that his personal enemies can be wiped out anywhere. The brave journalist Anna Politkovskaya was shot dead weeks before Mr. Litvinenko was poisoned; last year, opposition leader Boris Nemtsov was gunned down near the Kremlin walls.

This is not how normal states behave, and the rest of the world should no longer treat Russia as a normal state. Engagement at working levels has to continue, but the criminality of the Putin regime should disqualify him from the normal interactions of global affairs. He is an outlier in behavior; he should be treated as an outcast.