Regeni, a 28-year-old postgraduate student at Cambridge University, vanished in Cairo in January 2016. His body was found almost a week later and a post mortem showed he had been tortured before his death.
There was no immediate comment from authorities in Egypt. Egyptian officials have repeatedly denied any involvement in Regeni's killing.
The five suspects are all members of the National Security Agency and include a general, two colonels and a major, the source said. They are under investigation for allegedly kidnapping Regeni. No one has yet been named in connection with the killing itself.
Regeni disappeared on Jan. 25, 2016 - the fifth anniversary of the start of the 2011 uprising that ended the 30-year rule of Hosni Mubarak.
Italian and Egyptian investigators have been working together to try to solve the crime and have held regular meetings in Rome and Cairo to pool their information. However judicial sources in Rome told Reuters last week that Italy was frustrated by the slow pace of developments in Egypt. (Reporting by Domenico Lusi, Writing by Crispian Balmer, Editing by Andrew Heavens)
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