The mass shooting on Saturday in Buffalo in New York state is the latest in a series of attacks across the United States this year which caused multiple deaths.
However, the apparent racial motivation behind the murders, the age of the suspect arrested at the scene – just 18 years old – and the fact killings were streamed live on social media has generated shock across the country.
US president Joe Biden late on Saturday night said more needed to be learned about the background to the attack. Mr Biden suggested it represented “hate-fuelled domestic terrorism”.
“A racially motivated hate crime is abhorrent to the very fabric of this nation. Any act of domestic terrorism, including an act perpetrated in the name of a repugnant white nationalist ideology, is antithetical to everything we stand for in America. Hate must have no safe harbour”, he said.
Police were on Saturday investigating an 180-page document posted online in which the author set out a plan to attack a black district and to kill as many people as possible.
The author identified the semi-automatic rifle that would be used in the attack as well as details of his plan to shoot a security guard near the entrance at the supermarket before moving on to kill others inside.
The document essentially centres on a far-right conspiracy theory that holds baselessly that the white population in western countries is being reduced – or “replaced” – by immigrants as part of a deliberate plot.
The author of the document maintained he was inspired by the perpetrators of other white supremacist violent attacks in recent years including the killing of nine black parishioners in South Carolina in 2015.
The author said he had watched the livestream of this attack carried out by the perpetrator and had read his writings.