I think it was a Learjet. It had no trim or markings of any kind. It landed at Hilo, Hawaii on Friday morning, 2/18/2010 and parked in front of the CAP hangar, 100 feet from the National Guard hanger.
Within a short period of time two National Guard UH-60s spun up and did three touch-and-goes, in formation, inside the pattern and probably no more than 300’AGL maximum. Maybe two minutes a hop. They landed after a total of about ten minutes of engine time and shut down.
When I returned to the airport about an hour later the Lear was gone. We see a lot of AF1-type blue and white livery here because we are the best fuel stop between the mainland and Guam if you don’t want to be noticed. But I never saw an aircraft without markings before. I guess that someone with a lot of stars and his aide wanted their annual helo qual.