There is a very simple observation that if any outsider is killer why would he drag the body of hemraj to terrace and then lock the door and then escape..2nd point .. talwars have a small flat. not a bungalow that they were in deep sleep during the crime..So Whoever is the killer ..im sure talwars know about that..
There is one more guess...Hemraj killed Arushi. and was caught by talwars and they (with help of someone ) killed hemraj...i think this might true
