To quote the petition that you are all invited to sign:
In February of 2019, the Moscow State University mathematics PhD student Azat Miftakhov was arrested and detained for manufacturing explosives. Later these charges were dropped. As soon as he was released, he was arrested and detained for another unrelated crime: breaking a window in the office of United Russia, the ruling political party in the Russian Federation. We, along with the international civil rights society Memorial, consider Azat to be a political prisoner, unfairly framed due to his anarchist views. The court extended his pre-trial period multiple times — a year and a half in total — without reason. Law enforcement officials have tortured him, restricted his access to scientific literature, and threatened his relatives’ personal safety.
The Société Mathématique de France published an update on December 21, and called for its membership to sign the petition:
Le procès d’Azat Miftakhov approche de sa conclusion. Les débats sont prévus le 23 décembre. Le verdict devrait tomber peu de temps après.
Le 14 novembre 2020, la SMF a exprimé sa profonde préoccupation face à la détention prolongée du jeune probabiliste et activiste politique russe qui fut incarcéré début février 2019. Il est resté emprisonné depuis et a été torturé. Azat Miftakhov est accusé d’avoir cassé une vitre dans un bureau de la “Russie unie”, le parti politique au pouvoir. Il plaide non coupable.
UPDATE: Azat faces sentencing tomorrow (January 11). This article published in Novaya Gazeta refers to this letter to the organizers of the ICM, and to this letter by the President of the AMS. The petition has meanwhile been signed by more than 2700 mathematicians, and Azat has received support from the Unione Matematica Italiana and the Sociedade Brasileira de Matemática.