Cohen dropped the parachute that exploded.
3. Si Nuo may not have escaped, because he didn't have a plane. He thought that when dropping these parachutes, he used Kapit's plane hijacked by the rebels.
It should be Si Nuo's conspiracy to gather a group of children, because Si Nuo knows that as long as these children are his shield, the rebels can't act rashly. He miscalculated. Cohen killed those children in order to occupy Kapit faster, so it can be proved that she put those parachutes, and Katniss also shot the only bow and arrow at her chest to prove her anger.