SEYNE-LES-ALPES, France -- French President Francois Hollande said Wednesday that the case of the second black box of a German plane that smashed into a rugged Alpine mountain, killing all 150 people on board, has been found, but not its contents.
Meanwhile, investigators hoped the plane's cockpit recordings would help unlock the mystery of what caused the plane to drop unexpectedly and crash.
Speaking alongside German Chancellor Angela Merkel and Spanish Prime Minister Mariano Rajoy, Hollande promised that French investigators would do everything to determine the cause of the crash.
"We need to understand what happened," said Hollande, speaking in Seynes-les-Alpes, the town nearest to the crash site. "We owe this to the families."
The missing black box was the flight data recorder, which captures 25 hours' worth of information on the position and condition of almost every major part in a plane.
"At this moment people are on the scene still searching," Hollande said.
Hollande also said there could be no rescue because it was certain that all 150 people aboard the plane had perished in Tuesday's crash in the southern French Alps.
"This is a true tragedy, and the visit here has shown us that," Merkel said.
Crews were making their way slowly to the remote crash site through fresh snow and rain, threading their way to the rocky ravine. But CBS News correspondent Mark Phillips says the weather Wednesday was better than expected, bringing hopes that recovery efforts could speed along.
French Interior Ministry spokesman Paul-Henry Brandet said the overnight precipitation made the rocky ravine slippery, increasing the difficulty of reaching the steep area.
Phillips said retrieval of the victims would be the first priority for search crews, and it wasn't going to be easy. The plane came down in the most inhospitable, inaccessible terrain imaginable.
The orange cockpit voice recorder - dented, twisted and scarred by the impact - is considered the key to knowing why the Germanwings A320 lost radio contact with air traffic controllers over the southern French Alps then crashed Tuesday during a routine flight from Barcelona, Spain, to Duesseldorf, Germany.
French officials said terrorism appeared unlikely, and Germany's top security official said Wednesday there was no evidence of foul play.
Remi Jouty, director of the French aviation investigative agency, said some audio had been recovered by Wednesday afternoon, including sounds and voices. He said it was too early to draw any conclusions from the recorder, which takes audio feeds from four microphones in the cockpit and records all the conversations between the pilots, air traffic controllers as well as any noises.
Jouty said the plane was flying "until the end." He said the final communication from the plane was a routine message about permission to continue on its route.
Helicopters surveying the scattered debris lifted off at daybreak for a look at the craggy ravine. Emergency crews, meanwhile, traveled slowly over the steep, rocky terrain to the remote high-altitude crash site through snow and rain. In all, more than 600 rescue workers and aviation investigators were in the area, French officials said.
The crash left pieces of wreckage "so small and shiny they appear like patches of snow on the mountainside," Brandet said.
Investigators were zooming in on two key minutes Tuesday - 10:30-10:31 a.m. - said Segolene Royal, a top government minister whose portfolio includes transport. From then on, air traffic controllers were unable to make contact with the plane.
German Interior Minister Thomas de Maiziere told reporters in Berlin on Wednesday that "there is no hard evidence that the crash was intentionally brought about by third parties."
The plane, operated by Germanwings, a budget subsidiary of Lufthansa, was less than an hour from landing in Duesseldorf when it unexpectedly went into a rapid, eight-minute descent. The pilots sent out no distress call, France's aviation authority said.
Lufthansa CEO Carsten Spohr, himself a pilot, said he found the crash of a plane piloted by two experienced captains "inexplicable."
Investigators will use the cockpit voice and flight data recorders to map out and focus their work, said Alan E. Diehl, a former air safety investigator with the National Transportation Safety Board.
"Both will point you in directions of what is critical," Diehl says. "Based on what you learn from the recorders, you might focus on key pieces of wreckage."
The four possible causes of any crash are human error, mechanical problems, weather, criminal activity or a combination of two or more. Diehl says investigators will essentially work backward.
"You're usually dealing with a jigsaw puzzle with many of the pieces missing," he says. "You start eliminating things that didn't happen."
Lufthansa said two charter flights to France will be made available for family members who want to get as close as they can to the crash site. Locals in Seyne-les-Alpes offered to host the bereaved families because of a shortage of rooms to rent.
Germanwings cancelled several flights Wednesday because some crews declared themselves unfit to fly after losing colleagues.
"The management completely understands this, because we are a small family. Everyone knows everybody inside Germanwings, so it is a big shock for employees," said CEO Thomas Winkelmann.
He said the company had already contacted most families of the victims and was trying to reach the rest. He said victims included 72 German citizens, 35 Spaniards, two people each from Australia, Argentina, Iran and Venezuela and one person each from Britain, the Netherlands, Colombia, Mexico, Japan, Denmark, Belgium and Israel.
In Washington, the State Department said three Americans were presumed dead, including a U.S. government contractor and her daughter.
Some could have dual nationalities, for Spain's government said 51 citizens had died in the crash.
The victims included two babies, two opera singers, an Australian mother and son vacationing together, and 16 German high school students and their two teachers returning from an exchange program in Spain.
"Nothing will be the way it was at our school anymore," said Ulrich Wessel, the principal of Joseph Koenig High School in the German town of Haltern.
"I was asked yesterday how many students there are at the high school in Haltern, and I said 1,283 without thinking - then had to say afterward, unfortunately, 16 fewer since yesterday. And I find that so terrible," he added.
Paul Andrew Bramley, a 28-year-old from Britain, had been studying hospitality and hotel management in Lucerne and was flying to meet his mother before starting an internship on April 1.
"He was the best son. He was my world," said his mother, Carol Bramley.
In Spain, flags flew at half-staff on government buildings and a minute of silence was held in government offices across the country. Parliament canceled its Wednesday session.
Barcelona's Liceu opera house held two minutes of silence at noon to honor two German opera singers - Oleg Bryjak and Maria Radner - who took the flight after performing at the theater last weekend.