"Italy insists: we want the truth," said Italian Foreign Minister Paolo Gentiloni on his Twitter feed late yesterday, while prosecutors in Rome rejected the latest conclusions of the Egyptian probe.
Italian media and Western diplomatic sources in Cairo have voiced suspicions that Egyptian security services kidnapped and tortured to death the Cambridge University graduate whose mutilated body was found in Cairo in January.
On Thursday Egyptian police said they had identified people linked to Regeni's murder, after killing four members of a criminal gang and finding the victim's passport.
The four suspects are accused of concealing a crime and being in the possession of stolen material, a prosecution official said, adding they were taken into custody for four days.
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Regeni disappeared on January 25 in central Cairo. His body was found nine days later on the side of a motorway, badly mutilated and showing signs of torture.
Rome prosecutor Giuseppe Pignatone said in a statement that "details communicated so far are not satisfactory to shed light on the death of Giulio Regeni. Investigations must therefore continue."
"Italy will never content itself with anything less than the truth, the whole truth, without shadows or mystery," a source within the premier's office said.
Quoted by Italian press, Regeni's parents said they were "injured and bitter" at Egyptian authorities' latest attempt to explain their son's death.
Two of Regeni's friends quoted by the Corriere della Sera newspaper said that glasses and a quantity of cannabis apparently found by police in the student's room definitely did not belong to him.
The incident has threatened relations between Egypt and Italy, a strong supporter of President Abdel Fattah al-Sisi whose security services have been accused of abusing dissidents.