Claudia Matteini ruled that enough evidence existed to detain Amanda Knox, Raffaele Sollecito and Patrick Lumumba while the investigation into the death of Merideth Kercher proceeds, the Times of London said Friday.
Officials discovered the body of Kercher, 21, in her Perugia apartment last Friday partially naked with her throat slit.
Lumumba, a bar owner, denied involvement in the incident claiming 16 witnesses would state he was at work at the time of Kercher's death.
Knox, who shared the flat with Kercher, claimed Lumumba killed Kercher in her bedroom after Lumumba said he "wanted" her.
"I put my fingers in my ears so I could not hear (the screaming from the bedroom)" Knox is quoted in the Telegraph, noting she did not intervene.
Sollecitio, Kercher's boyfriend, said he had "smoked so much marijuana" he couldn't recall the evening's events.
Investigators found a knife on Sollecito "compatible" with the weapon used in the incident and discovered a bloody shoe-print also "compatible" with Sollecito's footwear.
Police officials are searching for a fourth suspect in the case after investigators found fingerprints not matching Kercher or the three main suspects, later reporting by the Telegraph said Friday.