On a Sunday night in February, 2007, “Dateline NBC,” the news show, aired a segment about the strange case of Alexander Litvinenko, a Russian dissident who died under mysterious circumstances in London. On the show, several guests argued that his death was an assassination, carried out on orders from Vladimir Putin. The Russian President denied any involvement in Litvinenko’s death.

Among the “Dateline NBC” guests who accused Putin was Paul Joyal, a former government official and an expert on Russian affairs. On a rainy night, four days later, Joyal pulled up to his house, in Adelphi, Maryland, and was attacked by two men. As he wrestled one of the men to the ground, he heard him say to his partner, “Shoot him.” The second man pulled the trigger on a 9-mm. pistol and hit Joyal in the abdomen, then pointed the gun at Joyal’s head and pulled the trigger. The pistol misfired, and then Joyal’s dog, inside his house, began to bark. His wife, also inside, turned on the lights. The two men ran off.

More than a decade later, with Russia’s covert activities in the United States facing intense scrutiny, it seems appropriate to raise the question: Was Joyal shot on the orders of the Russian state? And, more generally, does the Russian government kill people in the United States?

After months of treatment, Joyal recovered, but the crime has never been solved. The F.B.I. investigated Joyal’s attack, but he declined to share details of what it reported about its findings. Joyal told me that he believes one of Putin’s friends—“an oligarch”— arranged the shooting. Some Russia experts believe that he is right. “I think they were intending to send Joyal a message,” Paul Goble, a former senior analyst with the State Department and a friend of Joyal, told me. Goble noted that Joyal had been working to arrange for a Chechen activist to visit the United States—an effort that would have enraged the Kremlin. “He crossed a line you cannot cross.”

Russian agents have killed political opponents in Europe and the Middle East. An exhaustive investigation by a British parliamentary commission concluded that Litvinenko, the dissident, had been killed by Russian agents, “probably” on orders from Putin. Litvinenko, a former K.G.B. agent, had accused Putin of ordering the assassination of Anna Politkovskaya, a crusading Russian journalist who was murdered, in 2006. He also accused the F.S.B.—the K.G.B.’s successor organization—of bombing a series of Russian apartment buildings, killing three hundred people, in order to win public support for a large-scale war in Chechnya. In late 2006, Litvinenko had ingested polonium 210, which was likely dropped into a pot of green tea while he was meeting with two Russians at the Millennium Hotel. For twenty-two days, he suffered increasingly grotesque symptoms; first his hair fell out, then his organs failed. At last, he died. Two men were indicted in the United Kingdom for his murder, but the Russian government refused to turn them over.

A recent series of investigative articles by BuzzFeed examined the deaths of a number of Russian dissidents and Putin critics who died mysteriously in the United Kingdom. In November, 2012, Alexander Perepilichny, a Russian businessman, collapsed and died outside his home in Surrey. Perepilichny had been coöperating with Swiss authorities investigating the alleged theft of some two hundred and thirty million dollars by Russian tax officials, and he had told friends that he feared the Kremlin would kill him. An autopsy found traces in his system of gelsemium, a rare plant grown in the Himalayas that is fatal when ingested. According to BuzzFeed, a report prepared by American intelligence for Congress stated with “high confidence” that Perepilichny was assassinated on Putin’s orders.

But what about the United States? Goble, the Russia expert, told me that, during the Cold War, the United States and the Soviet Union sometimes assassinated each other’s spies and defectors, but not inside the opponent’s country. “In Soviet times, there were very clear rules of the game,” Goble said. “We never killed anyone on their turf.” He mentioned one possible exception: Walter Krivitsky, a Soviet agent who defected to the United States, in 1938, and later revealed Stalin’s plans to sign the infamous Molotov-Ribbentrop Pact with Germany, which cleared the way for the Nazi invasion of Poland. Krivitsky was killed with a bullet to the temple, in what the police labelled a suicide but many acquainted with Krivitsky alleged was murder.

Goble thinks that Putin has disregarded the old rules. He’s not alone: a number of cases in the United States have raised suspicions. One of those is that of Mikhail Lesin, who, on November 5, 2015, was found dead in his room at the DuPont Circle Hotel, in Washington, D.C., with—according to a Washington, D.C., Police statement—“blunt force” injuries to his head, neck, torso, arms, and legs. Lesin had been a powerful figure in Russia: a former Cabinet minister and adviser to Putin, as well as the founder of Russia Today, which acts as a propaganda platform for the Kremlin in the West. Vasily Gatov, a former senior media executive in Russia and a visiting fellow at the Annenberg School for Communication, at U.S.C., told me that Lesin had accumulated a large fortune and a number of opponents during his rise. “He had a lot of enemies,” Gatov said. After being fired by Putin, in 2013, he left Russia, moved to the United States, married, and had a child. “With the birth of his baby, it was important to him to be alive,” Gatov said. If Lesin had decided to coöperate with American investigators, that would be sufficient motive for someone to try to stop him, Gatov told me. “The idea that someone would want to silence him is pretty viable,” he said.

A yearlong investigation by the United States Attorney in Washington concluded that Lesin’s death was accidental, the result of a fall and of “acute ethanol intoxication.” Lesin had been drinking for days, the report said. The case was closed. Still, the report raised suspicions: Gatov told me that, since the birth of his child, Lesin had apparently stopped drinking altogether.

Without more evidence, we can’t really know. Sometimes, deaths that seem mysterious turn out to have innocent causes. In 2010, Sergei Tretyakov, a former high-ranking Soviet spy, died suddenly, at the age of fifty-three. From 1995 to 2000, he had posed as a diplomat at Russia’s mission to the United Nations, where he oversaw covert operations in New York City. Then he defected, and, according to Pete Earley’s book on Tretyakov, “Comrade J,” handed over five thousand secret cables to American officials.

Tretyakov’s death, at his home in Florida, attracted interest from the F.B.I. and C.I.A. But, according to Dr. Russell Vega, the chief medical examiner for Sarasota County, Tretyakov did not seem to have been the object of a nefarious plot. He died by choking on a large piece of chicken. How did that happen? The autopsy showed that Tretyakov was extremely drunk at the time. “It wasn’t subtle,” Vega said.