After the Snowden disclosures -- never mind the whole Room 641A business ( https://en.wikipedia.org/wiki/Room_641A ) -- I think the only safe assumption is bad faith on the part of both government and industry.

In fact, that's the whole problem with extrajudicial domestic spying. In defiance of the principles of both justice and logic, the innocent are presumed guilty, and the burden of proof is shifted to the skeptics.

There isn't anyway to know for sure but its extremely suspicious that they will not release the off switch despite already having developed it for the US government.

The only way there could ever be proof of such a thing would be from whistleblowers and that would be major news (or so I believe).