Two Afghans, aged 23 and 29, were arrested in Bari, southern Italy, on Monday on suspicion of planning attacks in Italy, the UK and France. A third member of the suspected network - allegedly a five-strong terror cell with links to Al Qaeda and Isis - was later arrested.
The investigation began back in December when the men were spotted taking "incriminating photos" of a Bari shopping centre.
A police search of their mobile phones uncovered other images of Bari's airport and port, as well as sites in Rome, Paris and London including hotels and tourist sites. These phones were Samsung Galaxy devices which police were able to access using Oxygen Forensic Suite 2015 software.
"It was clear these were not tourist images. They appear to have been scouting sensitive sites," prosecutor Roberto Rossi said at a press conference in Bari. The phones also contained images of Italian and Afghan military vehicles and weapons, as well as Taliban propaganda videos and "a series of chants traditionally sung in preparation for martyrdom", he said.
But a third phone, an iPhone 6 Plus, remains inaccessible to investigators.
The case has parallels with the high-profile battle between Apple and America's FBI involving the locked iPhone of gunman Syed Rizwan Farook who, along with his wife, shot dead 14 people in San Bernardino, California. Apple resisted a court order requiring the company to help investigators access the phone, arguing that adding a 'back door' into their software could be dangerous.
"We have encountered the same difficulty as the FBI," Roberto Rossi, one of the prosecutors, told a press conference in Bari. "This is a real problem … because the balance between protection of privacy and protection of people is a serious problem that must be viewed on an international level."
"The majority of evidence is found on electronic devices," he said.
The FBI managed to unlock the phone without help from Apple, saying they had had help from an "outside party" in ending the six-week legal battle, but Rossi told media that the Italian police did not have the same kind of money as the FBI to spend on the case.
However, there is a possibility that the US government could help Italian police. At the time, they said that the technique used to access Farook's iPhone 5C might also work on other models running the same software.
The three arrested suspects are due to appear in court in Bari on Thursday.
Italy's security level remains at level two, the highest possible in the absence of a direct attack.