Sidharth knew this because his gang and Mr. Anil’s had crossed paths and they still had unresolved issues between themselves, so it would seem that Mr. Anil had killed his parents to threaten The Silverton Mafia Gang which was being run by his father and his uncle at the time, Sidharth came across a transcript of a call made between Mr. Ajay and Mr. Anil, this must have been after the murder had been committed, it was as follows,

AJ: I know what you did Anil! I know what you did! I’ll report you to the police!

AN: what’re you talking about? You sound like a deranged person, are you...