The American website NBC News reported that the FBI's general counsel Dana Boente sent a letter to her counterpart at Apple on Monday, pointing out that though a court had given it permission to examine the phones' contents, it could not do so as the data was encrypted.
Boente's letter said: "Investigators are actively engaging in efforts to 'guess' the relevant passcodes but so far have been unsuccessful."
“We have the greatest respect for law enforcement and have always worked co-operatively to help in their investigations," the company said.
"When the FBI requested information from us relating to this case a month ago, we gave them all of the data in our possession and we will continue to support them with the data we have available.”
The last time the FBI approached Apple for help in decrypting data on an iPhone was in 2016, with the device in question belonging to a terrorist who had been involved in an attack in San Bernardino in California in December 2015.
In March 2016, the agency obtained a court order, asking the company to supply a new version of its mobile operating system, iOS, which did not have certain locking functions, so that it could attempt to guess the passcode on the iPhone 5C by using a brute force method.
When Apple resisted, the FBI came back with an order compelling the company to fall in line. After some to-ing and fro-ing, in March 2017, the FBI ended the stoush, saying it had gained access to the iPhone in question.
The current case has been made a mite more complicated than the 2016 one, as Alshamrani fired a round into one of the iPhones before he was killed.
The 2016 stoush led to a debate over the use of encryption and both the UK and Australia subsequently passed laws that allow for the creation of software solutions to gain access to encrypted data.
The debate was given a fresh lease of life last year when the US Attorney-General William Barr, Australian Home Affairs Minister Peter Dutton and UK Home Secretary Priti Patel wrote to Facebook chief executive Mark Zuckerberg, asking him not to extend end-to-end encryption, which is available through WhatsApp, to Facebook Messenger.
In December, during a speech to a global summit to tackle child sexual exploitation, Dutton hit out at Zuckerberg and Apple chief executive Tim Cook, accusing them of being "morally bankrupt on the issue of encryption and protecting children".
The Australian law, officially known as the Telecommunications and Other Legislation Amendment (Assistance and Access) Bill 2018, was passed on 6 December 2018, after a number of hearings conducted by the Parliamentary Joint Committee on Intelligence and Security. Several amendments were proposed, but none were adopted before the Labor Party voted along with the government to pass the bill.
Soon after, a review of the law by the PJCIS was announced with a reporting date of 3 April. But the only thing that this committee did was to put off any decision on amendments, instead asking the Independent National Security Legislation Monitor Dr James Renwick to review the law and report back by 1 March 2020.