Three migrants from Senegal and Nigeria have been arrested by police investigating the rape and killing of a girl whose death has been seized upon by the populist right.
The body of Desirée Mariottini, 16, was found in a derelict building in an area of Rome known for drug trafficking. She had been drugged and gang raped.
Right-wing Interior Minister Matteo Salvini hailed the arrests, condemning those behind the murder as "worms".
It would not go unpunished, he said.
Mr Salvini, who leads the anti-immigration League party, has spearheaded measures aimed at scrapping protection for migrants not given refugee status, as well as stopping NGO ships carrying rescued migrants from landing in Italy.
When he visited the scene of Ms Mariottini's murder on Wednesday close to Rome's main Termini station, he was given a mixed reception of cheers and insults. There were shouts of "jackal", an insult used by critics who have accused him of taking political advantage of human tragedy.
Investigators believe the victim fell unconscious for several hours last week after being given a cocktail of drugs by several people, and died of an overdose. She was sexually abused before she died.
Teenager's death feeds anti-migrant message
By Julián Miglierini, BBC News Rome
The slow pace of Italian justice will determine what happened to Desirée - how and why she was killed.
Details are emerging of her short life, marred by a broken home, substance abuse issues and institutional failings.
But in populist Italy there is no time for complexities. It is the headline-grabbing promises that work - and Matteo Salvini is a master at riding that wave.
He showed up twice in one day at the scene of the crime, and - even before the Senegalese men were arrested as suspects - he was already using the case to promise an iron fist in his fight against illegal migration.
That rhetoric is what allowed him to become Italy's most popular politician.
On his social media accounts, Mr Salvini, first as a candidate and now as a minister, has made a point of highlighting serious crimes committed by migrants across the country.
He pushes the idea that serious crimes such as homicide that are committed by migrants are contributing to an increase in violence in Italy - but the statistics from his own ministry contradict these claims.
Police believe as many as six people may have been involved in her death, including two Italians. A third suspect has already been traced.
They first arrested two Senegalese men, aged 26 and 42, who are described as undocumented migrants, and later picked up a Nigerian man aged 40. All three were suspected of murder, gang rape and supplying drugs, police said.
Further details of Ms Mariottini's last few days have been reported in Italian media.
After her parents split up she lived with her grandmother.
The family's lawyer said the day before she disappeared she had phoned her grandmother to say she was staying with a friend in Rome as she had missed her last bus.
Her friend said the teenager had been sold drugs in exchange for her mobile phone and had gone back to the traffickers in an attempt to retrieve the phone.
Rome Mayor Virginia Raggi, whose populist Five Star party shares power with Mr Salvini's League, has responded to the murder with a promise to increase police patrols and ban alcohol consumption in the streets after 21:00.