I've tried to figure out where the video was taken from and make estimates of the flight path...image from Google Earth attached.
At the start of video you can see a ferry dock (?). Notice there's a floating support half-way across the ramp to shore. I think the video was taken along the shore near the intersection of 20th and Avenue C.
If this is where the video was taken, the helicopter comes out of the vertical dive to the South-East of the camera, then proceeds North up the East River. It seems to disappear from view roughly offshore from the 34th street heliport. Any folks familiar with NY city that can validate these guesses?
I wonder if he was trying to return to the departure point? Or perhaps he get disoriented and thought he was continuing South towards the Williamsburg Bridge? If heading back to the heliport, wouldn't he have descended?