Guys listen, the gun Karan was carrying was not his service gun, it was the one those guys were carrying who trapped Monu in the jungle.
So even if Karan shot Monu, they can't trace it back to him. Whatever monu will say would be considered final in this scenario. So no Karan's job in danger sequence here.
I just think the purpose of this track is to burst Monami's bubble of her crush and to soften Karan towards Monami. Phir we know, monu will avoid karan and he would start falling for her. The usual approach.
They are doing the same with Sid and Sanj too, wish they spice things up for MoRan and add more layers to their story.
