unlock the mobile

Why it has taken almost a year the Civil Guard in getting to unlock the mobile of Diana Quer?

Diana Quer disappeared from A Coruña, Spain, in August 2016 and the only clue that has been obtained to try to locate it is her mobile phone, an iPhone 6 that a shellfish found in an estuary near the pier of Taragoña, in Rianxo. An iPhone 6 that had spent two months under water and was visibly deteriorated by, among other things, exposure to water from the estuary itself.

As soon as the mobile phone was found, the Civil Guard, specifically the Criminal Service, SECRIM, began the investigation to try to obtain as much information as possible from the phone. Until now, only the WhatsApp conversation history of Diana (thanks to a duplicate of the SIM and only acceding to the messages not received until the moment) but at last has been able to unlock the telephone, almost a year later. How did it take so long to get it?