A trace of blood belonging to American student Amanda Knox was found in her Perugia apartment that investigators believe dates back to the night her British flatmate was slain, news reports said Wednesday.

Investigators found the blood on a bathroom faucet and one of Knox's fingerprints on a glass, but the apartment was otherwise cleaned after Meredith Kercher, 21, was killed, according to a summary report by investigating magistrate Giuliano Mignini quoted by the ANSA news agency.

Investigators concluded that the blood was left on the faucet sometime between Nov. 1 and 2, when Kercher was killed with a knife wound to the neck. Investigators have concluded that Knox was in the apartment during that period although Knox herself hasn't disputed that.

"The visibility of the stain is such to exclude that it could have been left in the days before the crime since it would surely have been cleaned," investigating magistrate Giuliano Mignini wrote in the summary of his probe so far, ANSA reported.

Knox, 20, a University of Washington student from Seattle, has admitted in one of her several conflicting statements to prosecutors that she was in the apartment the night of the slaying, saying at one point she had to cover her ears to drown out Kercher's screams. She has denied any wrongdoing, however.

Knox and Kercher's DNA was found on a knife that investigators believe may have been the murder weapon; the knife was found at the home of Knox's then-boyfriend Italian Raffaele Sollecito.

Calls to Knox's attorney were not answered Wednesday.

Knox, Sollecito, and Rudy Hermann Guede, an Ivory Coast native, have been detained in the slaying. Guede is awaiting extradition to Italy after his arrest in Germany.

A fourth suspect, Diya "Patrick" Lumumba, a Congolese who runs a bar in Perugia, was released from jail for lack of evidence.

All four suspects deny any role in Kercher's slaying.

Guede has admitted that he was in Kercher's room the night she died, but said he didn't kill her and that an Italian who is trying to frame him did. DNA testing has confirmed that Guede had sex with Kercher the night of the murder.

Prosecutors have said Kercher was killed while resisting a sexual attack. Guede has denied he attacked Kercher sexually.

Kercher family attorney Francesco Maresca said Wednesday he believed that investigators had determined that a second autopsy would not be necessary on Kercher, letting her family in Britain bury her.

A hearing is scheduled Friday in Perugia to determine if Knox and Sollecito should continue being held. The judge who originally ordered them held after their Nov. 6 detentions said there was sufficient evidence to warrant their detention and that they represented flight risks.