As I explained, they were not in MSP approach air space. Approach only handles aircraft below 10,000 ft in most instances. Obviously Denver would need more airspace.
I quit 11 years ago and disposed of all of my old charts, Airman’s Guides, etc., so my memory may not be exact.
But approach would pay no attention to a flight at 37,000 ft. unless center called them and set up the descent with them.
I missed it if MSP center’s part in this has been described in any detail. We don’t know that they missed an aircraft flying through their airspace. My guess is that they did not miss it, that they were advised by Denver as well as seeing the flight and that they made attempts to contact them.
It will all come out.
By the way, I know not how busy MSP is nowadays, but when I flew into and out of there it was during the best days of NorthWest and it was a very busy airport. Plus there were a half dozen or so satellite airports also with instrument approaches which made for a busy time for controllers. So no controller would likely have time to think about a flight 27,000 ft above his territory.
From a thread about the F-16's this morning "Air traffic controllers reported the pilots initially failed to respond to commands as it passed from the air space controlled by the FAA Denver Center into the area controlled by the Minneapolis Center. The concern grew as the pilots ignored a command from the Minneapolis approach controllers to begin a descent for landing."
Thread has a news report that explains a little more about what ATC was doing or attempting to do if you haven't seen it yet. Still leaves some questions though.