A black box recovered from the scene and pulverized pieces of debris strewn across Alpine mountainsides held clues to what caused a German jetliner to take an unexplained eight-minute dive Tuesday midway through a flight from Spain to Germany, apparently killing all 150 people on board.

The victims included two babies, two opera singers and 16 German high school students and their teachers returning from an exchange trip to Spain. It was the deadliest crash in France in decades.

The Airbus A320 operated by Germanwings, a budget subsidiary of Lufthansa, was less than an hour from landing in Duesseldorf on a flight from Barcelona when it unexpectedly went into a rapid descent. The pilots sent out no distress call and had lost radio contact with their control center, France's aviation authority said, deepening the mystery.

While investigators searched through debris from Flight 9525 on steep and desolate slopes, families across Europe reeled with shock and grief. Sobbing relatives at both airports were led away by airport workers and crisis counselors.

"The site is a picture of horror. The grief of the families and friends is immeasurable," German Foreign Minister Frank-Walter Steinmeier said after being flown over the crash scene. "We must now stand together. We are united in our great grief."

It took investigators hours to reach the site, led by mountain guides to the craggy ravine in the southern French Alps, not far from the Italian border and the French Riviera.