Privacy concerns have been raised after police investigating a murder case in the United States issued a warrant for audio and other records from an Amazon Echo digital assistant in the accused's home.

Echo is an always-on digital assistant in the shape of a speaker developed by Amazon. It is capable of doing many tasks, such as answering questions, calling an Uber, ordering pizzas, playing music and audiobooks, reading news headlines, providing weather, traffic and other real-time information.

Now, officers in Bentonville, Arkansas, suspect it may also have witnessed a killing.