23-year-old prisoner Leonid Kats responded to Novaya Gazeta* from a pre-trial detention center. We publish his letter in full 18+. This material (information) is produced, distributed and (or) sent by a foreign agent of the Internet publication "NOVAYA GAZETA" or relates to the activities of a foreign agent of the online publication "NOVAYA GAZETA". Zoya Savatova: I heard about Leonid Katz, a graduate of the intellectual school and the higher school of economics, almost a year ago. There was information in the media that the young mathematician was charged under Article 275 of the Criminal Code of the Russian Federation ("Treason") in December 2025. Criminal cases under this section of the Russian Criminal Code are investigated and considered behind closed doors, so there are no details on the charges filed against Leonid Katz. According to certain information leaked to the media, the young mathematician was going to continue his studies in one of the European countries. Lawyers and family do not comment on the situation. I wrote to Leonid in the pre-trial detention center in Moscow-3, which is located in Krasnaya Presnya, through the FSIN letter service, I explained that I visited prisons in Moscow from 2008 to 2016, and asked him to tell how he settled into his new life, what books he reads, whether he succeeds in doing his favorite science, whether he receives letters from relatives and friends, and what he thinks about the prison in which he unexpectedly found himself. Leonid answered. Judging by the letter, this is a detailed person, he writes in detail, with details, at the same time, his text is lyrical and resembles "blank" verse. We publish the text of the letter in the author's edition. The link does not open? Read here *The Russian authorities consider him a "foreign agent".

23-year-old prisoner Leonid Kats responded to Novaya Gazeta* from a pre-trial detention center. We publish his letter in full 18+. This material (information) is produced, distributed and (or) sent by a foreign agent of the Internet publication "NOVAYA GAZETA" or relates to the activities of a foreign agent of the online publication "NOVAYA GAZETA". Zoya Savatova: I heard about Leonid Katz, a graduate of the intellectual school and the higher school of economics, almost a year ago. There was information in the media that the young mathematician was charged under Article 275 of the Criminal Code of the Russian Federation ("Treason") in December 2025. Criminal cases under this section of the Russian Criminal Code are investigated and considered behind closed doors, so there are no details on the charges filed against Leonid Katz. According to certain information leaked to the media, the young mathematician was going to continue his studies in one of the European countries. Lawyers and family do not comment on the situation. I wrote to Leonid in the pre-trial detention center in Moscow-3, which is located in Krasnaya Presnya, through the FSIN letter service, I explained that I visited prisons in Moscow from 2008 to 2016, and asked him to tell how he settled into his new life, what books he reads, whether he succeeds in doing his favorite science, whether he receives letters from relatives and friends, and what he thinks about the prison in which he unexpectedly found himself. Leonid answered. Judging by the letter, this is a detailed person, he writes in detail, with details, at the same time, his text is lyrical and resembles "blank" verse. We publish the text of the letter in the author's edition. The link does not open? Read here *The Russian authorities consider him a "foreign agent".