> What other services might be run, controlled, or surveilled by the US investigative authorities?
More boringly, and more simply, they hire people who work at Apple, Google, and so forth to exfiltrate data, create constant new bugs that will at some point be called a 0 day, and it goes on and on.
Apple and Google turn over data without subterfuge under FAA 702. That's what the Snowden leaks were about. There are APIs for the IC to fetch this data directly from the servers of Apple and Google without a warrant. They don't need to hire anyone.
More boringly, and more simply, they hire people who work at Apple, Google, and so forth to exfiltrate data, create constant new bugs that will at some point be called a 0 day, and it goes on and on.