Maybe it's not WHAT the neighbor saw. but WHOM...
TOTAL speculation... accident at home, excessive discipline gone awry.... TS calls her new bf (again, total conjecture) for help. He arrives, loads vehicle.
Smell test:
A MAN could better lift 90#.
TS could halfway genuinely say she doesn't know where he is.
Other children asleep, might not know or suspect a thing.
Neighbor didn't seem entirely sure he knew what he was looking at, right? He brought it to the dad in the morning, not straight to LE.
I think -- SPECULATION -- when Dad saw what he saw, it was crystal clear. Confirming infidelity and death all at once. That would bring a dad to his knees. Crushing.
HERO RIBBON goes to the neighbor... taking the time to review more images, from outside the target timeframe. Good hearted man....
Wishing for Gannon to come home "safe".... for closure... we ALL feel for this little boy.... sadly, we know how he's coming home..... it's our hearts that want him out of the cold, out of the dark and back with his parents, safe.
JMO