He has been identified by French authorities as German citizen Andreas Lubitz, 27, and his actions in the final minutes of the flight are believed to have caused the crash, Brice Robin, Public Prosecutor of Marseille, said Thursday at a news conference.
“The intention was to destroy the plane," Robin said, speaking mostly in French.
French Interior Minister Thomas de Maiziere said that investigators are focused on Lubitz' background and motives, though they have started to rule out any connection to a larger plot.
"There is no evidence of any kind terrorist background," de Maiziere said in a statement released Thursday.
Lubitz was a member of a flight club called Luftsportclub Westerwald in his hometown of Montabaur, Germany.
"Andreas joined the club as an adolescent, he wanted to make his dream of flying come true," the club said in a statement released to ABC News.
"He was able to realize his dream, the dream he now has paid for so dearly with his own life," the statement said.
An airline spokeswoman said Lubitz had 630 hours of flight experience and only 100 of those hours were on this particular model of plane, an Airbus A320. By comparison, a U.S. first officer would be required to have at least 1,500 hours of experience to get hired by an airline.
Investigators have been able to listen to the audio recording from inside the cockpit and the captain can be heard leaving the cockpit and then tapping on the door to re-enter but being denied, Robin said.
The banging on the door grows louder while the co-pilot can be heard breathing throughout, he added, suggesting he was not incapacitated before the Tuesday crash that left 150 people dead.
Robin said the co-pilot had no reason not to allow the captain back into the cockpit and he should not have gone silent on the radio to air traffic control.
"When you commit suicide, you die alone,” Robin said in response to a question. “With 150 on the plane, I wouldn't call that suicide.”
Editor’s note: A French prosecutor initially said Lubitz was 28 years old but a law enforcement official later determined that he was 27.