Congressional investigators are examining whether General Motors Co Chief Executive Mary Barra and other senior executives were more involved than they have publicly acknowledged as the automaker considered how to deal with a deadly ignition switch issue linked to at least 13 deaths, three sources familiar with the probe say. At issue is who knew about and was responsible for an internal investigation in 2011-2013 that eventually discovered the switch issue which has led to the recall of 2.6 million cars.