22-year-old mathematician Leonid Katz, a graduate of the “Intellectual” school for gifted children and holder of a bachelor’s degree from the Higher School of Economics, has been arrested on treason charges. For the previous two months he was subjected to so-called carousel arrests. Katz is accused of making donations to a charitable fund that assists Ukrainian children. After his detention, he was tortured — T-invariant learned this from two sources.
On September 30, Leonid Katz left home with his luggage to head to the airport. The recent graduate of the mathematics faculty at the Higher School of Economics was planning to continue his studies in a French master’s program. The detention came out of the blue: plainclothes officers took him away in an unmarked car, without presenting any documents or stating the grounds for his detention or arrest.
T-INVARIANT BACKGROUND
Leonid Katz graduated from Moscow’s “Intellectual” school, where he repeatedly won prizes at academic olympiads during his studies. He also attended the mathematical school of Yakov Abramson. The school’s website still features a profile of Leonid Katz, describing him as coming from a “mathematical” family — his grandfather is a professor of mathematics. After finishing school, Katz entered the Higher School of Economics. In 2025, he completed his bachelor’s degree at the Faculty of Mathematics, defending a thesis closely related to dynamical systems, in which he studied the classical Kuramoto model and its modifications. The work developed ideas about the connection between the analysis of these dynamical systems and the Möbius group. At the same time, he worked in bioinformatics and mathematical processing of cognitive brain research results. His instructors describe him as an exceptionally bright and versatile gifted student. After defending his bachelor’s thesis, Leonid Katz was accepted into several master’s programs in Russia and France, including top universities: MIPT, Skoltech, École Normale Supérieure, and Paris-Saclay University.
As Leonid’s acquaintances told T-invariant, neither he nor his family suspected any surveillance.
For the next 24 hours, his whereabouts were unknown, so Leonid’s parents were forced to file a missing person report with the police. They soon received a response: their son had been detained by FSB officers. Two sources informed T-invariant that on the first day, Leonid was interrogated with electric shocks and other forms of physical abuse. After the torture, he signed blank sheets of paper. Katz was then handed over to police officers, who arrested him for 15 days. Leonid was held in the Sakharovo special detention center [a facility on the outskirts of Moscow primarily used for administrative detainees and foreign nationals facing deportation — T-invariant]. He spent a total of two months there. According to the BBC Russian Service, on October 1 he was charged under articles on “profane language” and “disobeying police.” The ruling of Moscow’s Cheryomushkinsky District Court stated that Katz used profanity in a public place, insulted passersby, and attempted to provoke a conflict with police officers. Leonid served 15 days, but upon release from the special detention center he was detained again. This time, the Gagarinsky District Court noted that on October 16, at a bus stop, Katz used profanity and harassed citizens. A third 15-day administrative arrest was imposed on Katz on November 1 by the Zyuzinsky District Court for refusing to show his passport to police. And on November 18, the press service of Moscow courts reported that Katz had been sent to the special detention center for 15 days for allegedly swearing near the Mars pond in northern Moscow.
However, as one of his acquaintances says, since October 1 Leonid had not been able to leave the special detention center, and it is unclear how he could have violated public order in different districts of Moscow. “Everything stated in the court rulings about his arrests is untrue. These were carousel arrests,” the source says.
This scheme is well known to human rights defenders and lawyers: it is often used by Russian security forces before formally opening a criminal case. Carousel arrests allow a person to be held in custody longer than the law permits. During this time, investigative bodies coordinate the criminal case with direct or indirect superiors and gather materials, explain human rights defenders from the First Department [a project specializing in defending those accused of treason and related offenses. — T-invariant]. And when the investigation has collected enough materials or the necessary statements, the suspect is often charged under one of the serious charges — for example, treason, espionage, or terrorism. This method has been widely used — from opposition politician Ilya Yashin to street musician Naoko.
In early December, the Meshchansky Court of Moscow received a motion from the investigation to remand Katz to custody under Article 275 of the Criminal Code (treason). From the Sakharovo special detention center, Leonid was transferred to a pretrial detention center. “Mediazona” drew attention to the case file. The information has now been removed from the court’s website.
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The specific accusations against Leonid have not been made public. However, the actions of the security forces almost exactly repeat the case of physicist Artem Khoroshilov.
Security services obtain information about donations to Ukrainian citizens, then “put under surveillance” the source of the transfer, fabricate and falsify evidence against him to support charges carrying the maximum penalty. The repressive nature of these cases is indicated by the fact that security forces try to attract as little attention as possible to these criminal proceedings, intimidating the relatives and lawyers of the accused, hiding any details from the press and human rights defenders, and making no attempt to turn the cases with huge sentences into high-profile show trials.
Clearly, it is impossible to present Artem Khoroshilov or Leonid Katz as real traitors to the homeland either to the broad public through the media or even to colleagues from other security departments and agencies. If there were compelling evidence of an actual crime, it would be possible to proceed without torture and “carousel arrests” according to the procedure established by law. Otherwise, it remains only to quietly report another “uncovered treason” at the cost of a ruined life and career of a talented scientist.
Unlike a whole series of criminal cases under the article on providing support to an extremist organization (donations to the Anti-Corruption Foundation), cases of treason over donations to Ukrainian citizens or organizations are becoming a new trend — a formalized response by the FSB to the expansion of the treason law adopted in July 2022.
Leonid Katz’s lawyer and family members do not comment on his case.