Honestly, it might have been privately owned. When I lived in a more rural area we used to have private helicopters buzz the roads, homes and just
about anything else.
I see completely unmarked, matte-black helicopters fly over my house fairly frequently.
It was especially apparent after 9/11 - There were literally at least five a day for about a week.
I know why too - I live about five miles from Mount Weather, an acknowledged underground government base that has a FEMA operation on the surface and something entirely else (and entirely secret) under.
It's possible there is an underground base near you if you see these helicopters. Do some more research into that field.
Originally posted by emsed1
After looking at your pictures I can tell you it's the Sky8 Bell 407 from Portland.
You can see it HERE