After the morning assault in the town of Macerata, the suspect got out of his auto, made a fascist salute with a tricolour Italian flag draped over his shoulders and shouted "Viva Italia", or "Long Live Italy", and "Italy for Italians", media reports said. The news agency ANSA reported that Traini had run as a candidate for the anti-migrant Northern League in a local election previous year in the city of Corridonia.
Six people including "people of colour" have allegedly been injured, four of them seriously, media reported.
Italy votes in national elections on 4 March, with immigration one of the key issues.
Hospital officials say one of the six Africans wounded by a far-right Italian gunman has been treated for their injuries and released.
The suspect in Saturday's shootings - identified by Carancini as Luca Traini, 28 - was apprehended by police while making a fascist salute in front of a monument to war victims.
The victims included five people from Nigeria and one from Gambia, according to Lt. Col. Andrea Corinaldesi of the Carabinieri. "There is an armed man in a auto who is shooting in the city". The Nigerian suspect, who was denied asylum past year but has remained in Italy, has refused to talk to police.
The teen's remains were found on Wednesday in two suitcases, two days after she walked away from a drug rehab community. Macerata's mayor has urged citizens to stay indoors Saturday while the suspects remain at-large.
Police have not said how many people were wounded in Saturday's shootings.
A Nigerian migrant has been arrested in connection with the death.
Local reports are linking the two incidents. While the shooter was still active, police told residents to stay inside and ordered public transport halted.
Right-wing politicians have been using Pamela Mastropietro's killing to promote their anti-migrant message as part of their campaign for the general election.