I think its Ashu because, as a member of the Aggarwal house he is also a suspect, so why is he of anyone in chanrge of the case. They should have someone else in charge because Ashu himself is a suspect. I think this way because we are being told to think that its someone else for exaple Vandi Massi because at this moment she is shown ver suspicious, and there there is Om. Perhaps, the murderer is someone that had nothing to do with her, so taht way he wont be a suspect. And there is no way in hell, that Ashu would be under this suspicion because one hes a police officer and two he didnt really have anything to do with Tanu.
And then there is Aditi. She is under most suspicion to me because, she was realated to Vijay Aggarwal, so how could she have not known Andy being related to them, and if she did why didnt she tell Tanu or he members of the Aggarwal family.And she was the one who showed him to Tanu through a magazine, obviously she is hiding something. And think of it this way, Ekta never brings someone into the soap opera unless there is something that they will bring to the climax, in this case, she hasnt really done anything other than claiming Parvati as her mother, and since that track is over why cant she leave, obv there is something else, that Ekta wants to do with this character, perhaps being a murderer.