Court said there was enough indications of guilt to keep an American girl, her Italian boyfriend and a Congolese bar owner in jail as suspects in the murder of British student while the investigation continues.
Judge Claudia Matteini said there were "serious indications of guilt" that warranted keeping the three in jail for up to a year while the investigation continues. She also warned in a 19-page ruling that each of the suspects posed a flight risk.
The three suspects, all under investigation for murder and sexual assault, have denied involvement in the killing, according to their lawyers.
Under Italian law, suspects can be kept behind bars without being charged if a judge rules there is enough evidence to jail them and there is a chance they might flee, repeat the crime or tamper with evidence. Prosecutors may later seek to indict the suspects and put them on trial.
The judge said in her ruling that, if released, the suspects could try to leave Italy.
"They could easily have left the territory of the state to escape the investigation," the judge wrote, noting that Lumumba is from Congo, Knox is American and Sollecito could have enlisted his girlfriend's help to flee.
Kercher's body was found in the apartment she shared with Knox, and police said she died fighting off a sexual attack. The coroner said Kercher was stabbed in the neck.
Matteini said it was not yet clear who might have dealt the fatal blow, but said Sollecito's footprints were found in Kercher's room, and identified the murder weapon as a knife with an 8.5-centimeter-long (3.3-inch-long) blade that the Italian usually had with him.
However, the judge wrote that, when questioned by investigators, Knox said Lumumba was also in the room and that he had killed Kercher.
In her reconstruction of the incident, the judge said Knox, who worked for Lumumba at his Perugia bar, let the two men into the apartment with her keys.
"Then something went wrong," Matteini wrote. "The two (men) demanded some kind of sexual act, which (Kercher) refused to do. She was then threatened with a knife, which Sollecito always carried with him, and with which Meredith was stabbed in the neck."
One of Sollecito's attorneys, Luca Maori, said he planned to appeal the decision.
"We didn't expect it," he said. While saying he had not yet read the ruling, he said the defense team was "perplexed" by the judge's decision.