It's unknown whether Lubitz planned his actions in advance, Robin said. But he "took advantage" of a moment in which the pilot left the c*#kpit and "activated the descent," which can only be done deliberately.
It's also unclear whether the pilot entered a code to try to get back into the c*#kpit, or whether Lubitz "put the lever on lock," which would have prevented the code from working, Spohr said.
What is known is that screaming could be heard on an audio recording for the final few minutes of the flight.
Death was instantaneous for those on board when the plane plunged into the mountains, Robin said.