The man suspected of shooting worshippers at a San Diego synagogue appears to have posted a rambling online document which referenced “cultural Marxism”, a phrase commonly used in far-right circles and in mainstream political discussions.

Authorities have identified the suspect who opened fire in the Poway building as John Earnest.

The gunman killed a woman and injured three others, including a rabbi who was shot in the hand.

A person using the same name as the suspect posted an antisemitic screed online shortly before the attack.

The document is filled with far-right tropes and white supremacist ideology.

The suspect also appears obsessed with his descent and bloodline and with race war conspiracy theories.

He discusses antisemitic tropes, including the false suggestion that Jewish people control the media and financial system.

In an incoherent list of why he hates Jewish people, the suspect also blames them for their “role in cultural Marxism”.

In the aftermath of the shooting, journalists took to Twitter to highlight the use of the phrase.

“Today’s killer said one of the reasons he hated Jews was ‘for their role in cultural Marxism’,” Jason Wilson, a writer and journalist, wrote.

“Every shameless hack who has used that term in earnest should retire in shame.”

Batya Ungar-Sargon, an editor at US newspaper The Forward, also noted the suspect’s use of the phrase.

Online, “cultural Marxism” has been widely used among far-right groups operating on 4chan, 8chan, YouTube and other sites.

In these corners of the web it is overwhelmingly used to suggest that “cultural Marxists” – a term applied to certain politicians, members of the media, academics and companies – are responsible for undermining traditional society.

It was also used by far-right terrorist Anders Breivik, who killed 77 people in Norway in 2011.

“Cultural Marxism” is a phrase which originated after the 1917 Russian revolution.

Marxist thinkers such as Antonio Gramsci theorised that the reason the revolution was not being repeated in other nations was because the cultural conditions needed for such a movement were absent.

Story continues

The philosophers thought that shaping culture would play a key part to any socialist revolution, a theory which was developed by academics at the Frankfurt school in the 1940s.

Today conspiracy theorists use these origins, and the fact that many Frankfurt school thinkers were Jewish, as a basis for claims that “traditional” society is being undermined.

Despite the fringe origins of “cultural Marxism”, the phrase has recently been used in mainstream discourse in broader discussions about freedom of speech.

Suella Braverman, a Conservative MP, was criticised after she used the phrase while speaking to anti-EU think tank the Bruges Group in March.

“As Conservatives we are engaged in a battle against cultural Marxism, where banning things is becoming de rigueur, where freedom of speech is becoming a taboo, where our universities – quintessential institutions of liberalism – are being shrouded in censorship and a culture of no-platforming,” she said.

The language has also been used by Jordan Peterson, a psychologist with an increasing public platform.

“Make no mistake. The transformation of ‘cultural Marxism’ into a catch-all meme, one that is so imprecise and ill-defined, has meant that it can be weaponised by the most sinister and nefarious of individuals online, without consequence or reprimand from social media platforms,” journalist Hussein Kesvani wrote in The Independent last month.

“Its lack of definition – coupled with a poor understanding of its place in the online spaces that informs so much of our modern political conversations today – means that its existence in a context of rampant online antisemitism, anti-Muslim sentiment and fervent nationalist populism – is treated as secondary, if not inconsequential.”

The suspect in Saturday’s attack also appears to have filled his document with false allegations and what is known as “shitposting” – where online jokes and memes are used to derail outsiders’ understanding of a document.

His victims were worshipping on the last day of Passover, exactly six months since 11 people were gunned down at Pittsburgh’s Tree of Life synagogue – the deadliest attack on Jews in US history.