Europe Lufthansa CEO: It will take time to understand what led to plane crash

The chief executive officers of both Lufthansa and Germanwings paid their respects at the plane crash site in France Wednesday.

Claude Paris/AP

Lufthansa's chief executive said Wednesday it will take "a long, long time" to understand what led to a deadly crash in the French Alps last week — but refused to say exactly what the airline knew about the mental health of the co-pilot suspected of deliberately destroying the plane.