The two men had joined an online neo-Nazi community before planning the attack.
Musk’s tweet “smelled of antisemitism...[and] immediately brought a flood of antisemitic conspiracy theories,” the Foreign Ministry said.
The teenager was arrested in April last year and later charged with joining the far-right international online group called Feuerkrieg Division (FKD).
The neo-Nazis marched with flags adorning the Celtic cross, a popular symbol of white supremacy.
The shooter wore a patch with the letters "RWDS," an abbreviation for "Right Wing Death Squad."
Federal police requested the order after Telegram didn't comply with a court decision to handover data about two neo-Nazi groups on the app.
The photo shared of the incident saw the men performing a Nazi salute, holding a frame of Hitler as well as two balloons both taking the shape of the letter "H" (short for "Heil Hitler).