Han Xiao had gone to the road the night before when the troops were camping at the battleground. He had planted a trap using the corpses of Pan Kuang and Ji Jie to lure Colonel Carl out of his vehicle. The moment Carl stepped out of his command vehicle, Han Xiao had the opportunity to snipe him down.
Additionally, he had placed a blank landmine beneath the bodies to scare the troops out of their formation so that he could get a better shot at Colonel Carl from the distant cliff.
Killing a high-ranking Hesla officer in front of everybody was bound to raise suspicion from the Hesleans. They could probably deduce that it was Han Xiao who did it based on the use of the two bodies, but Han Xiao was not at all worried. They had no concrete evidence to proof that he was guilty. As long as Division 13 denied it, all Hesla could do was protest diplomatically. They could never hold Han Xiao accountable.