Authorities said the six wounded - five men and one woman - appeared to be random targets in various parts of the city of 43,000 in Italy's central Marche region.
Police in Macerata, Italy, arrested a suspect in the drive-by shootings that injured seven people on February 3.
After the assault, the Mr Traini got out of his vehicle, allegedly made a fascist salute with an Italian flag draped over his shoulders and shouted "Viva Italia", or "Long Live Italy", and "Italy for Italians".
The suspect, identified locally as Luca Traini, 28, might have acted in what is likely a revenge attack following the alleged murder of an Italian woman, in connection for which a male immigrant from Nigeria has been detained.
Police who raided his mother's home found far-right literature, including a copy of Adolf Hitler's manifesto "Mein Kampf" and a book by fascist dictator Benito Mussolini.
Police said Traini, who has a neo-Nazi symbol tattooed above his eyebrow, admitted to carrying out the drive-by shootings and had shown no remorse. "I was talking and laughing with three other people" when she was struck by the bullet, she told the Turin-based newspaper. At least one of them is said to be in a serious condition.More news: Aaron Donald wins defensive player of the year
"He drove around in his auto and when he saw any black people he shot them", Marcello Mancini, a Macerata resident, told Reuters television. "I can't wait to get into government to restore security, social justice and serenity to Italy", he said on Saturday. Stay out of the way and avoid open places, ' the local police said in a posting on its official Twitter account.
Macerata, Italy is the scene of a mass shooting targeting black people.
More than 600000 mainly African migrants have reached Italy by boat over the past four years, and thousands have perished on the journey.
Matteo Salvini, the head of League, has campaigned on deportation of migrants and has used Mastropietro's slaying in campaign rhetoric ahead of the March 4 national elections.
Mr Salvini is pledging to deport 150,000 migrants in his first year in office if his party wins control of parliament - drawing sharp rebukes that he is using the migrant crisis to foment xenophobia for political gain.
Commenting on the incident, Italy's Prime Minister Paolo Gentiloni warned that "the state will be particularly severe against whoever thinks of feeding the spiral of violence".