My car shows "last seen" on its Bluetooth connections. The murderer in this case was an invited friend; it's hardly implausible he's connected to Bluetooth there.

> I'm interested in evidence that this type of data extraction took place.

That they obtained access to the Echo's internals via Amazon is evidence. It sounds like you want proof of a very particular bit of data being in it, which I'd guess the FBI etc. aren't going to provide here.