Far-right supporter Luca Traini, 28, has been named by authorities as the suspect, accused of opening fire on five men and one woman from Ghana, Mali and Nigeria on Saturday in Macerata, a small town in central Italy.
Italian newspaper Corriere della Sera quoted the suspect as telling investigators that his attacks were triggered by the murder of an 18-year-old Italian woman, allegedly by a Nigerian asylum seeker.
A copy of Adolf Hitler's manifesto Mein Kampf and a book by fascist dictator Benito Mussolini were found at his mother's home.
Minister of the Interior Marco Minniti said the shooting had been prompted by "racial hatred".
"It's not easy to live in a town where somebody shot six black people. We are all scared,"James Nosakhari a relative of one of the victims, told AFP.
"You would never believe something like this was possible, this kind of thing happens in big cities," said Fabrizio Compagnucci, a newspaper seller in Macerata.
Italians will vote next month against a backdrop of populist gains and a rise of the far-right in Europe, with migration a central issue.
"The racist rampage that poisons the elections," read the headline of one Italian newspaper on Sunday.
The country is a favoured landing point on Europe's southern coastline for migrants making the perilous journey across the Mediterranean, often aboard unseaworthy boats, to enter the continent.
But 2017 was a turning point for Italy: the country went from large-scale arrivals in the first six months to a sharp drop-off, thanks to a controversial agreement between the EU and Libya.
The arrival of 630,000 migrants since 2014 has created fertile ground for anti-establishment and anti-immigration parties.
"Macerata is really a welcoming city. Men have always integrated well," Giovanni Lattanzi, national coordinator of the Human Solidarity Group NGO said.
Suspect Traini, who has a fascist-inspired tattoo, was a candidate in local elections last year under the banner of the anti-immigration Northern League.
"Someone who shoots is a delinquent, irrespective of the colour of his skin," said Northern league chief Matteo Salvini after the shooting.
On Saturday evening Italian Prime Minister Paolo Gentiloni called for calm, insisting "hatred and violence will not divide us".