Next you will see that Riddhima suspects Kabir and Anupriya that these people already know each other. That is why we see that Riddhima starts searching against him a lot, only then does he get the same school bag and uniform of Kabir which he pretended was 5 years old when Kabir was then. But that bag is capable of that bag which was purchased 2 days in advance.
And from this, Ridhima comes to know that this bag is not very old, it is two to three days old. That is why they know everything that they have done deliberately. After that Kabir goes there and he starts clapping. And Kabir says that you have come to know all this, I knew you could find it all but never thought so soon.
Kabir says that on that day you have made the biggest mistake by bringing Ragini to me. After that Riddhima says if you hit Ragini, yes I have killed Ragini. After that Riddhima says how can I make such a big mistake because you have left Ragini after that Kabir says that I can do anything I can kill you too and he pushes her into the swimming pool.