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The organization founded by Aleksei A. Navalny, the Kremlin’s most prominent political opponent, presented what it called new information to support its claim that he was poisoned.

By Anatoly Kurmanaev

Reporting from Berlin

Aleksei A. Navalny, the Russian opposition leader, suffered from heavy vomiting and convulsions shortly before he died in an Arctic prison last year, according to what the organization he founded called new information it had collected.