Found a hi-res picture.
They write that the flight altitude was 25..37 km.
It was equipped with the compressed helium tanks to maneuver up and down (and thus, choose the preferred wind direction to maneuver horizontally).
So, was shot down when lowered down to ~20 km on the helium reserve depletion.
(Not posting the link as it's too emotionally political.)
Also, they say the local citizens have watched AA missile launches at Billings (MT), but failed due to the flight altitude and poor target for their effective guidance.
The debris have sunk at ~14 m depth, and probably will be fished out soon.