When a victim dies a gory death with terrible attacks with a weapon mutiple times , the criminal profilers suspect that the murder took place because of sex.It could be either because of illicit relationships, or jealousy (in sex) involved. The very first attempt to understand this case , even by such a stupid police like Noida police , was "illicit relationships". Killing of a 14 year old girl in the night in her bedroom involved a motive to rape her is credible and could be the only motive.
The Dr.parents are a bunch of stupids. The house has no security, outsiders are coming in at the dead of the night. And no security outside the house to stop or to ask questions. The case is difficult to prove in a court of law unless CBI secures direct and independant evidence other than Krishna's confession to the crime. They have to arrest the third person, and get confession and also evidence from Rajkumar who is very much involved. Krishna wanted the blame to go on Rajkumar and it might be possible that Rajkumar did not know that Krishna would kill Aroushi so quickly.
If the Dr.Talwar came out of his room , hearing the commotion,he would have been stabbed to death along with his wife.
So learn a lesson from this incident (all north indian people) and raise the dogs , keep them inside and keep out the servants , out of the house.
I think our older generation people were much intelligent people than us. In olden days servants were more than today.