Vitaly Churkin, Russia’s ambassador to the United Nations, died suddenly in New York earlier this week, apparently of cardiac arrest.

Churkin, Russia’s envoy to the U.N. since 2006, reportedly became ill at his Russian Mission office in Manhattan on Monday and died at New York-Presbyterian Hospital. He was to turn 65 the next day.

The New York City medical examiner said more study is required into the cause and manner of Churkin’s death, though federal law enforcement has said it does not believe there was any foul play.

Still, because Russia is no stranger to political murders, the sudden death of a Russian official automatically raises suspicion. So while Churkin may indeed have died of natural causes, some have noted that it follows several other recent deaths of Russian officials, all occurring suddenly or under mysterious circumstances — including a man who is believed to have helped former M16 spy Christopher Steele compile his bombshell dossier on Donald Trump’s links to Russia.

On Nov. 8, the day of the 2016 United States election, Russian consular duty commander Sergei Krivov was found dead on the floor of the Russian consulate in New York. Though police had initially said he died of “natural causes,” a Buzzfeed report revealed mystery surrounding Krivov’s sudden death. Krivov, who was found with a head wound, was initially said to have fallen to his death before consular officials changed the story and said he had suffered a heart attack.

In December, Petr Polshikov, a senior Russian diplomat who served as the chief adviser to the Latin American department at the ministry, was found dead in his Moscow home with a bullet wound in his head.