Police on Monday named a fourth suspect in the Meredith Kercher murder as an Ivory Coast-born semi-professional basketball player, Rudy Hermann Guede.
Police say Guede, 21, was the third man in the flat of the victim in the early hours of November 2.
Forensics experts have identified him from a bloody fingerprint on Kercher's pillow, police say.
Police have been looking for Guede for several days.
He is believed to have left Perugia for Milan the day Kercher was killed.
An international arrest warrant was issued for Guede on Monday.
Kercher's American flatmate Amanda Knox, Knox's Italian ex-boyfriend Raffaele Sollecito and Democratic Republic of Congo pub-owner Patrick Lumumba have been in custody since the murder.
Traces of DNA from Kercher and Knox have been found on a knife belonging to Sollecito, a student at Perugia University.
Knox, a student from Seattle, has accused Lumumba of the murder.
Sollecito says he was working on his computer from the evening of November 1 till the early hours of November 2.
Police received the results of tests on Sollecito's computer on Monday but did not issue a statement about them.
Sollecito's lawyer said they confirmed his client's alibi.
Kercher, 22, was found with her throat cut on November 2 in the house she shared with Knox and two others.
Knox, Sollecito and Lumumba are being held on suspicion while investigations proceed.
They have not been charged with involvement in the crime.
According to unconfirmed reports, Guede was stopped in Milan before and after Kercher's murder, first after a theft and later because he was carrying a small quantity of drugs.
The 1.79-metre Guede played guard for the 'UISP Pallacanestro Perugia' basketball team in Italy's C1 third division until the 2004-05 season, police said.
Former team mates described him as ''a great lad with a great passion for the game, always on time for training, always ready to help others''.
His former club chairman, Roberto Segoloni, said Guede was ''more than perfect''.
He said he thought it was ''premature'' to link him with such a serious crime.
Guede came to Italy as a five-year-old to join his father but moved out when a Perugia businessman's family offered him a foster home when he was 17.
The businessman's son made friends with the Ivorian at an open-air basketball court.
He left the affluent family when he turned 18 to join some of his other relatives in Lecco north of Milan.
Guede later returned to Perugia and worked as a gardener in a farm-tourism restaurant run by his foster family.
Earlier, he reportedly held down bar jobs to support himself while doing hotel and computer courses.
Guede broke off relations with the family in August.
The businessman's daughter told ANSA Guede was a shy and introverted youth who never showed signs of violence.
''He was like an extra brother for us,'' she said.
Guede's adoptive mother reportedly broke down in tears, repeating ''It's not possible, it isn't possible''.
