Some of the smartphones seized from four men suspected of coordinating a string of robberies across Japan had almost no data left inside, indicating attempts to hide evidence linking them with the crimes, investigative sources said Wednesday.

Japanese police are stepping up their investigation into Yuki Watanabe, 38, and three others who were deported from the Philippines last week. They have been arrested on suspicion of theft in connection with scam cases targeting elderly people in Japan that took place before the robberies began last year.

The men are suspected of having remotely coordinated the robberies from the Philippines, where they were being detained at an immigration facility.

A total of about 15 smartphones and tablets were confiscated while the four were at the facility. They are believed to have bought privileges there that enabled them to run the operation.

Photo taken Feb. 8, 2023, in Manila shows vehicles transporting Yuki Watanabe and Tomonobu Kojima, two of the four Japanese men suspected of being behind a string of robberies across Japan, for their deportation to Japan from the Philippines, where they were detained on local charges. (Kyodo) ==Kyodo

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Some of the devices were successfully unlocked and analyzed but were found to be close to what appeared to be an unused state, with hardly any data storage use, the sources said. The Metropolitan Police Department suspects the devices may have undergone a factory reset to hide information.

The police will attempt to recover the lost data and analyze the remaining devices, hoping to shed light on the suspects' alleged involvement in both the scam cases and robberies.

In the robberies, those who actually broke into houses are believed to have received instructions via the encrypted Telegram messaging app, including the addresses of the victims, from a person or persons using the pseudonyms "Luffy" and "Kim."