Don't forget the "Alexa" thing is an actual IC. Just like the xbox, Echo is in low-power sleep mode most of the time and not processing or forwarding anything. The doodad that processes wake words is the only thing doing anything; that's why the wake word is fixed, because it's processed locally. It's only the stuff you say after you address Echo/Alexa that gets clouded, that's where the data mining comes from. If Echo/Xbox/Siri/Home actually sent every word spoken within 20' of them over the internet for inspection the data would be completely unmanageable.

In theory.

I do buy into the theory. If it was otherwise, it'd take a few minutes with a packet inspector to learn the truth, and nobody has suggested that.

Most likely, unless dude said, "Alexa, I'm being murdered" Amazon probably has nothing and they are [rightfully] objecting to an overbroad request. If the cops wanted 30 seconds or 30 minutes of activity I'd bet Amazon would comply, but turning over everything pertaining to a dead person? Unnecessary and overbroad.