The report comes almost a year after co-pilot Andreas Lubitz crashed Germanwings Flight 9525, killing all 150 on board.
Investigators said co-pilot Andreas Lubitz, suspected of deliberately crashing a plane in the French Alps in March, practiced entering the fatal descent settings the same day as the crash.
The Germanwings crash on Tuesday was not the first of its kind.
Investigators found the note when they searched Lubitz's flat.
Andreas Lubitz reportedly spent 18 months receiving psychiatric treatment during pilot training for German airline Lufthansa.
French prosecutors offered no motive for why the young German co-pilot crashed his plane.
Many of the messages celebrate the presumed deaths of Catalans who were on the flight.
Data from the black box, which was found on Tuesday morning, is currently being analyzed.
The two American victims are from Virginia, according to family members.