ROME, Italy (CNN) -- Forensic police investigating the killing of Meredith Kercher in Italy say they have uncovered more evidence tying the British student's American housemate to the scene of the crime.
Alberto Intini, Italy's chief forensic officer, said traces of Amanda Knox's blood had been found "mixed together" with Kercher's blood in a sink in the bathroom at the villa they shared.
Intini said blood belonging to the two women was also found on a box of cotton swabs on the side of the sink. He told CNN that drops of Kercher's blood were also found on the bathroom floor.
Kercher, 20, was found half-naked with a stab wound to her neck Nov. 2 at a villa in Perugia, where she was studying.
Knox, 20, from Seattle, Knox's Italian boyfriend, Raffaele Sollecito, 23; and Ivory Coast native Rudy Guede, 20, are all being held in connection with the case.
All three deny any involvement in the murder.
A fourth person, Patrick Lumumba, 44, has been released from jail for lack of evidence but remains a suspect.
Prosecutors have already uncovered a number of pieces of evidence which they say link Knox to the scene of the crime, including a blood stain found on the faucet of the bathroom sink that matched Knox's DNA.
Intini said the new evidence was found in a separate part of the same sink, although he did not specify where.
Asked why it had taken so long to come to light, he said forensics had uncovered over 200 "organic" pieces of evidence from the murder scene and the process of identifying where they all came from was taking a long time.
Prosecutors insist that both Knox and Sollecito were at the villa the night of the killing.
In the early weeks of the investigation police found DNA belonging to Kercher and Knox on a knife found at Sollecito's apartment. Prosecutors say a bloody footprint located next to the victim's body matched shoes owned by the Italian.
Guede is the only suspect to have admitted being at Kercher's villa the night she died. He admits having sex with her but claims she was killed by an unknown assailant.
He was extradited back to Italy earlier this month after fleeing to Germany. E-mail to a friend
CNN's Flavia Taggiasco contributed to this report.