Another theory would be that they were delivering the device for Apple to crack on their premises. This is based on the assumption that Apple could crack it (gi

Another theory would be that they were delivering the device for Apple to crack on their premises. This is based on the assumption that Apple could crack it (given as has been stated elsewhere that it is an older device without the secure enclave) but that they refused to hand the tools to do so over, and wanted to perform the crack themselves and the FBI, given the choice between a lengthy legal battle and getting the information on the device quickly, have given in to Apple. In which case either the device was unlock very quickly or if there's an equally short visit some time later, it's the FBI picking up the device again.