I'd suggest you to read news articles, esp from different sources. It will clear all the doubts.
Ambulance was called soon after. The boy died in the hospital.
The death took place because of the access bleeding that can happen to anyone, or no one. The rangers could not guess the boy, who was sitting and talking, was going to die so quickly.
Except for one young paranoid ranger, none in the team was expecting any firing. He was to be thrashed/harassed, and not shot at. The guy who shot the boy took everyone by surprise.
One shot can be accidental. Two, and it is deliberate.
That is why one of the rangers, who somehow got over the shock, immediately stopped it by saying "It's enough!".
It was shocking and accidental for the rest of the team, but quite deliberate on the part of that hotheaded young ranger.