The newspaper identified the officer as Lieutenant Lev Stupnikov, communications chief of a battalion in the 36th Motorized Rifle Brigade. It reported that he began serving near Vuhledar in November 2023 and, according to its account, supplied Ukrainian forces with unit positions, radio frequencies and combat plans.
Stupnikov also disabled equipment, the Journal reported: he switched off surveillance cameras and altered the voltage in the batteries of drone control panels so the drones failed mid-mission. In one episode he accidentally transmitted the coordinates of his own shelter and came under fire, but survived.
The largest single episode cited by the paper was a February 2024 strike on a Russian troop formation near Volnovakha. Stupnikov passed on the coordinates of the training ground in advance and, once about 120 to 150 people had assembled there and commanders had arrived, sent a photograph to the Ukrainian side. He then withdrew to a wooded strip, citing an upset stomach, according to the Journal. The strike killed 68 service members, including ten officers and the brigade commander, Colonel Gusein Musayev, and wounded about 60 more.
In May of that year he passed on the coordinates of the basement of a former hotel housing two assault units. A subsequent strike killed 20 people.
Stupnikov made contact with the Ukrainian side through his mother, Tatyana Yantsen, the Journal reported. She took part in protests against Putin and, after the invasion began, put up anti-war posters in Omsk and, together with her son, approached rights activists who helped Russian soldiers desert. In February 2024 she wrote to Ukrainian blogger Dmitry Karpenko, who worked with Ukrainian military intelligence, asking him to help her son leave the army. Through him Stupnikov began passing on information; according to the paper, he declined the offered payment.
On the night of July 6, 2024, the lieutenant crossed the front line along a route through mined terrain prepared by Ukrainian troops. In captivity he handed over a phone and passwords that let the Ukrainian side keep receiving imagery from about a dozen Russian drones and surveillance cameras for several more months.
Stupnikov was then met by Denis Kapustin, commander of the Russian Volunteer Corps, who suggested he become a communications specialist. The officer agreed two days later. According to the Journal, he is now taking part in combat against the 36th Brigade, in which he previously served.
By the summer of 2024 the command had begun to suspect an informant was at work. One of the commanders said the unit appeared to have acquired its own "Stirlitz," the Journal reported.
Stupnikov's story became public in September 2025 after a two-hour interview with Karpenko. That same month he was placed on a federal wanted list, and investigators visited relatives in Omsk. His mother and younger sister left Russia for Ukraine through Moldova in February 2025, crossing the border on foot. Stupnikov's wife, Yelizaveta, stayed in Russia and, in comments to state media, called her husband's action a betrayal.
After the interview, fighters from the Aida group of the Akhmat special forces announced the start of a "hunt" for the defector. Similar threats were made against another defector, Maxim Kuzminov, who flew a Mi-8 helicopter to Ukraine in August 2023 and was killed in Spain in February 2024. Stupnikov says he took Kuzminov's fate into account when deciding whether to stay in Ukraine.
Russian sources had earlier reported that Stupnikov's actions led to the deaths of more than 200 service members.