He went on to tell the newspaper, which has strong links to the centre-left party, that "those who justify incidents like the one in Macerata throw open the door to a return of fascism".
Ths suspected shooter has received a wave of support from "ordinary people", his lawyer said on Wednesday.
Luca Traini, who shot five men and one woman from Ghana, Mali and Nigeria in the central city of Macerata last Saturday, said the "trigger" was the murder of an Italian woman allegedly by a Nigerian asylum seeker.
"These messages of solidarity continue to arrive, from all parts of the political spectrum -- often from ordinary people and also from left-wing friends from Macerata and also obviously from right-wing people with the same ideology as Luca," his lawyer Giancarlo Giulianelli said.
"The messages mostly come from regular people who want to write letters or send money. Some even support the act itself, as though they were happy that he did it.
Police stand guard during investigations at one of the sites of the shooting. Photo: Giuseppe Bellini/AFP
"There are people who say 'let me know your IBAN (bank details) so I can send money', but my client, although he thanks everyone for the messages, doesn't intend to have any financial support because he wants it... to be sent to help Italian families in difficulty."
And in Rome, a large banner reading 'Onore a Luca Traini' (Honour to Luca Traini) was photographed on a bridge over the Tiber river.
Traini, a 28-year-old security agent, awaited police draped in an Italian flag after the shootings in a country where immigration is a hot-button issue a month ahead of elections.
READ MORE: 'It could have been me': Shooting highlights racial tensions ahead of Italy election
Giulianelli said his client 'snapped' a day after a Nigerian asylum-seeker and drug dealer was arrested in the same town in connection with the death of an 18-year-old woman, whose dismembered body was discovered in suitcases.
The Nigerian man is still being held on suspicion of for concealing and showing contempt for a body, but not for homicide, due to insufficient evidence. The cause of the woman's death has not yet been verified, with the suspect saying she died of a drug overdose. A second man is also being probed for allegedly selling drugs to the 18-year-old woman, who had left a rehabilitation facility just two days before her death.
"[Traini] went to the gym but then immediately changed his mind because he had this profound hatred inside of him. He lost it, that's what he said. 'I lost it and I wanted to kill black drug dealers'. That was his version," Guilianelli added.
"Leave aside the politics -- Luca was a marginalized person with problems related to his life that exploded with this act.
"The act obviously had a racial element so it highlights Luca's political ideology. But it was the act of a person who really isn't very well.
"Luca is not a fascist criminal, he is a boy who needs help," his lawyer insisted, saying people on the left and right swung from exaggerating to denying the problems posed by migration, whose solution "cannot be that given by Luca."
Traini has a fascist-inspired tattoo and left a Mussolini votive candle near the spot where Mastopietro's body was found. He is a member of the far-right Northern League, the junior ally in a centre-right coalition that is currently leading opinion polls ahead of a March election. He also ran in local elections last year.
Both Northern League leader Matteo Salvini and coalition ally Silvio Berlusconi have said the shooting was "non-political". Salvini said that "the moral responsibility of every incident of violence that happens in Italy is that of those who have filled it with illegal immigrants", while Berlusconi called immigration "a social bomb ready to explode".
Interior Minister and PD politician Marco Minniti earlier said the shooting was motivated by "racial hatred", and that the attack was part of a culture "of right-wing extremism with clear reference to fascism and Nazism". His party colleague, Justice Minister Andrea Orlando, visited the two wounded shooting victims who were still in hospital on Wednesday.
Plenty of members of the public and Macerata residents have denounced the shooting too, including the family of the 18-year-old who was found dead.
Anti-racism and anti-fascism campaigners have however cancelled a demonstration planned for Saturday after Macerata's mayor asked for protests to be paused, in order to avoid "divisions or possible violence" and give the city time to heal after the two horrific crimes. Demonstrations had also been planned by the neo-fascist CasaPound party and the extreme-right Forza Nuova.
In late 2017, parliament voted to outlaw fascist propaganda, including souvenirs and other products seen as celebrating fascism or Nazism.