Two Senegalese nationals aged 26 and 43 were reportedly held overnight. A third suspect, a 40-year-old Nigerian, was detained today.
The three are expected to be charged with group sexual violence, voluntary manslaughter and drug dealing. All three are reported to have previous convictions for drug dealing.
Police in Rome are still hunting at least one other suspect, local media reports.
Investigators believe Desiree was drugged and then gang raped while unconscious before she died.
Though the exact circumstances and cause of the teenager’s death are yet to be confirmed, an autopsy revealed that she had been under the influence of drugs and had been sexually assaulted.
An anonymous call was made to emergency services at 3am on the 19th of October, local media reported.
Flowers and candles have been laid outside the building in a tribute to Mariottini, and local residents have painted the walls with red hearts and the words ‘Justice for Desirée. San Lorenzo does not forget you’
“Now I want justice for Desiree. I don't want this tragedy to happen to other girls,” said the victim's mother, Barbara Mariottini, at her home in Cisterna di Latina, south of Rome.
The Mayor of Rome, Virginia Raggi, has announced a day of mourning for the city to coincide with Mariottini’s funeral. The date has yet to be announced.
On Twitter she announced that Rome would be 'stepping up controls' in San Lorenzo and raising the drinking age. She also said squats in other areas would soon be demolished.
Violenze come quella che ha subito #Desiree sono inaccettabili: https://t.co/31fN5eOFT3 A San Lorenzo vieteremo consumo di alcolici dopo le 21 e intensificheremo i controlli insieme a nuovi agenti.
ps Dopo Ostia procederemo con abbattimenti degli immobili abusivi dei Casamonica. pic.twitter.com/dKpqbSGoOO
— Virginia Raggi (@virginiaraggi) October 24, 2018
Interior Minister Matteo Salvini was quick to seize on the murder case, criticising Rome's local government and threatening to have part of the area bulldozed.
He visited the scene of the crime twice yesterday, with protesters preventing him from entering the building.
Even before the Senegalese men were arrested as suspects, he was already using the case to promote his fight against illegal immigration.