A resident of St. Petersburg. According to the investigation, he was an active member of the Right Sector, known under the name Sever. On 24 March 2022, Kazantsev was taken into custody. This happened after the operatives found him among Ukrainian prisoners of war. After his detention, the NTV TV channel published a video of his confession. According to his mother, he made the confession as a result of torture, which led to the fact that he had to have his toes amputated. In court, Kazantsev denied involvement with Right Sector. On 28 November 2023, he was sentenced to 12 years in a strict regime colony on charges of participation in the activities of an extremist organisation, possession of weapons and participation in an armed formation. On 19 March 2024, the court of appeal reduced the sentence by one month.