The March 24 crash killed all 150 aboard, including two Americans. All the victims represented a total of 18 countries.
Officials from Lufthansa, the noted Germanwings parent airline, are "speechless that this aircraft has been deliberately crashed by the co-pilot," CEO Carsten Spohr said.
It's unknown whether the co-pilot planned his actions in advance, Robin said. But the co-pilot, 28-year-old German national Andreas Lubitz, "took advantage" of a moment in which the pilot left the cockpit.
Screaming could be heard on the audio recording only in the last few minutes, and death was instantaneous for those on board when the plane crashed, Robin said.
Lubitz was not known to be on any terrorism list, Robin said.
The co-pilot "activated the descent" of the plane when he was alone in the cockpit, Robin said. That can only be done deliberately, he said.
The plane, en route from Barcelona to Dusseldorf, was flying at a cruising altitude of 38,000 feet before its six- to eight-minute descent into the side of a 3,000-foot-high mountain began.
The most plausible explanation of the crash is that the co-pilot "through deliberate abstention refused to open the cabin door ... to the chief pilot and used the button" to cause the plane to lose altitude, Robin said.
The audio recording showed Lubitz’s breathing to be steady, with no sign that he had a heart attack or other medical issue. He had only about 100 hours of experience on the type of aircraft he was flying, but he had all the necessary certifications and qualifications to pilot the aircraft alone, the prosecutor said.
The bodies of the Germanwings crash victims will not be released until all DNA identification work has been done -- a process likely to last several weeks, Robin said.
Robin emphasized that his conclusions were preliminary.
Finding the plane's second "black box,” the flight data recorder, will also be critical to understanding the mystery of what went on inside the jet. Spohr said Wednesday that there's a high probability it will be found.
The Germanwings media office told CNN the captain of Flight 9525 had more than 6,000 hours of flight time. He has been with Germanwings since May of 2014 and had worked with Lufthansa and Condor before then.