I am not sure in anyone posted this, but I looked up the music in the NZ shooting video.
1:20 to 4:50 is a song called Serbia Strong by Razni Ivodjaci. It appears to be anti-fascist in nature.
4:50 until he enters the mosque is The 1777 British Grenadieres March.
When he gets into his car to leave, he is listening to Fire by Arthur Brown.
Also, he leaves the car open and unsecure with weapons and ammo inside while the music is playing. There are people nearby who could easily investigate and take his weapons.