THE self-proclaimed racist believed to have killed 49 people at a New Zealand mosque during Friday prayers apparently opened fire with rifles covered in white-supremacist graffiti and listened to a song glorifying a Bosnian Serb war criminal.

Trying to understand what motivated the slaughter may be difficult, as some of the material posted by Brenton Tarrant - to appear in court on Monday - resembles the meme-heavy hate speech prominent in dark corners of the internet.

He even seemingly randomly referenced a prominent YouTube user before carrying out the attack. However, beneath the online tropes lies a man who matter-of-factly described himself in writing as preparing to carry out a terrorist attack before opening fire on Muslims who had gathered to pray.

The gunman’s soundtrack as he drives to the mosque includes an upbeat-sounding tune that belies its roots in a destructive European nationalist and religious conflict. The nationalist Serb song from the 1992-95 war that tore apart Yugoslavia glorifies Serbian fighters and Bosnian Serb political leader Radovan Karadzic, who is jailed at the United Nations war crimes tribunal in The Hague for genocide and other war crimes against Bosnian Muslims.

A YouTube video for the song shows emaciated Muslim prisoners in Serb-run camps during the war. “Beware Ustashas and Turks,” says the song, using derogatory wartime terms for Bosnian Croats and Muslims.

When the gunman has finished in the mosque and returns to his car, the song Fire by English rock band The Crazy World of Arthur Brown can be heard blasting from the speakers. The singer bellows: “I am the god of hellfire!” as the gunman drives away.

At least two rifles used in the shooting mention Ebba Akerlund, an 11-year-old girl killed in an April 2017 truck-ramming attack in Stockholm. Akerlund’s death is memorialised in the gunman’s apparent manifesto. It inspired what he sees as his war on those who oppose Western civilisation.

The number 14 is also seen on the gunman’s rifles. It may refer to 14 Words, which according to the Southern Poverty Law Centre, is a white supremacist slogan linked to Adolf Hitler’s Mein Kampf. He also used the symbol of the Schwarze Sonne, or black sun, which “has become synonymous with myriad far-right groups”, according to the centre.

In photographs from a now deleted Twitter account associated with the suspect that match the weaponry seen in his live-streamed video, there is a reference to Vienna 1683, the year the Ottoman Empire suffered a defeat in the siege of the city at the Battle of Kahlenberg. Acre 1189, a reference to the Crusades, is also on the guns.

Four names of famous Serbs who fought against the 500-year rule of the Ottomans in the Balkans, written in the Cyrillic alphabet, were also seen on the gunman’s rifles.

The name Charles Martel, who the Southern Poverty Law Centre says white supremacists credit “with saving Europe by defeating an invading Muslim force at the Battle of Tours in 734”, was also on the weapons. They also bore the inscription Malta 1565, a reference to the Great Siege of Malta, when the Maltese and the Knights of Malta defeated the Turks.