A Review Commission annulled the charges of murder against Chima Alinno and Brian Minthe.
It also reduced the charge of gang rape to sexual abuse aggravated by the minor age of the victim.
Both suspects’ charges of drug dealing were upheld.
They remain in jail.
Mariottini was allegedly drugged, gang-raped and left to die in an abandoned building in Rome's San Lorenzo district last month, in a case that shocked the nation.
A review hearing will be held today for Mamadou Gara, the third man arrested in relation to the case.
A 36-year-old Roman, Marco Mancini, was also arrested as a suspect on Sunday.
He was detained for allegedly selling drugs, including mixes containing quetiapine, with minors suspected of being among his clients.
He may have given Mariottini the drugs that killed her.