we heard a sound inside the building. >> pelley: anton gerber has worked at pelindaba for 30 years. of the plant's emergency control center. he was in the control room when masked men broke in. >> gerber: there's a crack in the door. and i looked through this, and i saw this four armed gunmen entering the passages is coming straight to us in the control room. >> pelley: you could see that they were carrying handguns? >> gerber: yeah. >> pelley: all four of them? >> gerber: all four of them. >> pelley: the men had breached a 10,000-volt fence, passed security cameras, and walked three-quarters of a mile to the control room that monitors alarms and responds to emergencies. gerber called the security office, just three minutes away. >> gerber: i immediately said to them they must come and help us. "we're under attack. there's four armed men inside our building." the first guy who stepped into the office, he said to me, "why do you phone?" he was shouting at me, "why do you phone? why do you phone?" >> pelley: in english? >> gerber: yeah, in english. and i was still so surprised, you kn