The problem being faced by those trying to break into iPhones – both criminals and authorities – is that the device is in its most secure state after a restart. It is in this Before First Unlock (BFU) state that the user's data is fully encrypted and almost impossible to access.
Apple's handsets indicate that passcodes are required after a restart, while iPhones in After First Unlock (AFU) states can be unlocked using just Face or Touch ID. Some data is unencrypted and easier to extract with certain tools in the AFU state.