I think it's Pihu
The Reasons:
1. When Priya came for chutha at shergill house and when neha was howling on priya , they had showed pihu's expressions , she was behaving like the person who is quite but have many things in mind .
2. When the CD of party arrives in KM and Khush taken that CD , That time also the trio i.e Mamaji, sid and juhi are all over smiling without any fear on their faces and were sitting with confidence and smiling faces as if they don't have any fear from that CD.
3. Sid and Mamaji has always used others and now another name added to them is Juhi, they all used to do things by " dusron ke kandhon pe rakh kar bandook chalana" so that's why may be they have filled pihu's mind in between party and by that pihu has killed sammy .
4. Since Cvs has shown earlier also during Varun's death no punishment was given to Pihu when she was the reason for such death so by this another death track because of and by pihu's hands Cvs can give punishment to Pihu this time by sending this character to mental asylum.
But in all this again the trio will come clear, Cvs may have planned something for them too since they are the roots of all miseries and problems. Juhi first claims that she used to love Ram and now when Ram is sent to jail and is announced the death penalty then the same lady is sitting on dinning table carefree with a content smile on her face as if she is on cloud nine by this judgement and waiting for having her tongue twisting on delicious meal.
But one thing is there in all this the greatest loss happened to Neha and Vikram plus Ram and Priya too had lost their first child or as they say their love symbol in some way as she is destroyed in all manners and now this is un-effect able whether pihu is alive or not because when she is standing for the reasons of two murders and when her heart and soul is ruined to depth then her life is just not worth for anything. Her father is in jail and is given death penalty but the madam is in no mood to leave thinking about herself and try to think about her father . As she say she hates her mother but loves her father a lot and when Ram has fulfilled her each and every wish even by breaking his relationship with his wife for her wishes and now that girl left her father in this state and is thinking about herself only, her emotions, feelings are everything to her and nothing else matter to her . It's looks likes she hasn't Love Sammy at any point but only love herself all the time and still doing the same.
Ram is not in jail and getting punishment for murder of sammy but is getting such punishment for loving her daughter to the core and trusting and helping people blindly. He is a gentleman and have given love to each and every person in his life sometimes he has given love and care to them by going out of limits and is getting punish for that only.
But it is also obvious that he will get free soon since he is the hero and a positive character so Cvs just can't end this role like this by giving death penalty in a false case, If cvs really want to end this character then they have chosen other means but not like this , so it is obvious that Ram will soon be free and the real culprits will get their correct deserving places soon.