In the video of the security forces, the man says that he works as a software engineer in an educational institution - according to his social networks, this is the Belarusian National Technical University.
According to what the security forces say, he published his opinions about the situation in Ukraine in the comments. Judging by the published screenshots, there is nothing radical there. For example, a man says that many Belarusians support Ukraine, and the dead Russian soldiers are occupiers in a foreign land, so they are not very sorry.
