The ACLU wants to know what arguments the government made to demand encryption be broken and why they were rejected. While a US District Court in California rejected the government request in September, no reasons were made public.
The hearing of the case itself was closed to the public and was reported by Reuters, quoting sources.
The case is of interest in Australia, because the Australian Government could make such a request to Facebook after its proposed encryption bill, currently before the Parliamentary Joint Committee on Intelligence and Security, is passed. Under the bill, Facebook would have no option but to agree.
The Messenger voice data was sought by a joint task force of the US federal and state governments which is investigating the MS-13 international crime gang.
Under American law, telecommunications companies have to give law enforcement authorities access to calls, but if the data is sent over Internet infrastructure by an app, then that app is not covered.
The US Government was attempting to force Facebook to rewrite the Messenger software so that it could gain access to the suspect's voice conversation which is encrypted from end-to-end.
MS-13 or Mara Salvatrucha is a gang that had its origins in Los Angeles in the 1980s and spread to other parts of the US, Canada, Mexico, and Central America.
The ACLU motion said: "The documents sought through this motion arise from a reported government effort to wiretap private communications that are ordinarily inaccessible to anyone, but the individuals who participated in the conversation."
And it added: "The government's request... is the latest in a years-long effort by the Department of Justice to undermine technology providers' use of various kinds of encryption to protect individual users' privacy."
Arguing for the release of the court documents, the ACLU said there was a great deal of public interest in knowing which law had been interpreted and how it had interpreted.
The rights body made reference to the Apple case of 2016, where the FBI sought to compel the company to create a new version of its iOS operating system so that the agency could gain access to the contents of an iPhone 5C owned by one of two terrorists who killed a number of people in San Bernardino, California, in December 2015.
Apple refused and the case went to court, But the FBI called off proceedings, saying that it had gained access to the smartphone in question by using methods devised by a private software company.
The documents sought by the ACLU are:
- any sealed docket sheets;
- any court orders on sealing requests;
- any judicial rulings associated with the proceedings mentioned; and
- any legal analysis presented in government submissions incorporated, adopted or rejected implicitly or explicitly in such judicial rulings.
Thanks to Ars Technica for a link to the ACLU motion.