I have a question:
How is a helium filled, tethered balloon, even close enough to the ground to be boarded by anyone?
And if the brother saw him go in, why did he untether the balloon after that?
Supposedly, the balloon was tethered in the family’s backyard. The neighbor reports that the two brothers were up on the roof with cameras and that they obviously believed that their brother was inside the balloon.
That sheds some light on this, I think. Maybe they talked their baby brother into the balloon, untied it, and got out their cameras to see what happened.