"Interrogator": "Okay, so it was written that So who did Karan initially assume was calling, and how did the caller respond when Karan expressed his suspicion that it might be a prank call?", 
"Interrogee": "Initially Karan assume that it is from stranger and he continue to talk with him while the stranger started talking about strange things like that he know everything about his daily routine like he knows where he goes gym, and how much he drinks and what time he drinks, what he eats, when he eats and everything else then Karan suspected might be his best friend rajat. But later it was confimed that was some stranger"