World Officials search for Germanwings pilot's motivation

Medical documents and ripped-up sick notes from a doctor suggest 27-year-old Andreas Lubitz may have hid an illness from his employers at Germanwings. But without a suicide note investigators can't be sure what was going through the pilot's mind.

A disgruntled worker shoots up a workplace. A student opens fire at a high school. A pilot crashes a planeload of people into a mountainside.