kyiv during russia s occupation and most were initially held here in a sprawling industrial site. the russian forces used it as a kmand command post. this is where they were kept? yeah. reporter: ukrainian prosecutor alexander zeus shows necessity conditions those captured people were forced to endure. a small, dark, cold room. people were packed together here, he says, hands bound, eyes taped. this place was where they took people. they were trying to get the toilet they need to walk on legs of somebody else. because too much people. reporter: he says people came and went. some spent weeks here. someone tried to keep track of days by scratching marks on the wall. he says all the people who came through this room had only one thing in common they were civilians. several people who were kept here tell us they were