Amazon is doubling down on its refusal to turn over voice records from an Echo device to Arkansas police, who believe the digital voice assistant may help solve a hot tub murder from last November.

In a new filing in Arkansas state court, Amazon claimed records from the Echo should receive special protection under the First Amendment since what owners say to the device—and the answers its assistant “Alexa” provides—are a form of free expression.

“At the heart of that First Amendment protection is the right to browse and purchase expressive materials anonymously, without fear of government discovery,” said Amazon, adding that Echo voice records could reveal information about a person’s health or political views.

The new filing comes two months after Alexa’s role in a murder investigation became national news. The case turns on the murder of Victor Collins of Bentonville, who was found floating in the hot tub of his friend, James Bates, where he died of strangulation and drowning. Bates is the prime suspect in the case, and police seized his Amazon Echo device as part of the investigation.

While Alexa devices on their own don’t contain a record of conversations, Amazon does create a record on its servers of everything users ask, as well as the answers Alexa provides. It’s those server records the Arkansas police wish to obtain. While it’s unlikely anyone asked, “Alexa, how do I hide a body?” the records might contain other clues about what happened at Bates’ house that night.

In its filing, Amazon says it has complied with the police request to preserve the voice records from Bates’ Echo, but that it should not have to turn them over unless police show a compelling need as well as a strong connection between Bates and the device.

Amazon’s argument reflects the heightened protection the Constitution affords when free speech is at stake. In the Bates case, Amazon is not saying the police have no right to the records—only that they have to make a very strong case that they need them. Otherwise, there’s a risk police could begin demanding records from Echos or similar devices, such as the Google Home, willy-nilly in any investigation.

This is not the first time Amazon has sought to throw up a First Amendment shield around its customers’ activities. In a 2010 case involving tax collectors in North Carolina, the company successfully argued it should not have to turn over customers’ purchase histories. A court in the case agreed that what people buy on Amazon reflect information about their private lives—and making such information easily accessible to police could chill free expression.

The Alexa hot tub affair is shaping up to be an important test case of traditional First Amendment rights, such as those involving library or bookstore records, and how they should apply to an age when people turn to their devices for information.

Finally, Amazon’s filing contains another important piece of information about privacy: The company points out that police seized Bates’ phone and, if he had installed the Alexa app, they could have been able to obtain the voice records that way. (Bates did not install the app).

You can read Amazon’s legal argument, spotted by Forbes, in full here (I’ve underlined some key parts).

This story originally appeared on Fortune.com. Copyright 2017