The CBI has said that Nirav Modi's aide Vipul Ambani was fully aware of the fraudulent Letters of Undertaking (LoUs) issued by former PNB official Gokulnath Shetty. The agency said the LoUs were recovered from Firestar Group's office, where he was the President (Finance). Vipul Ambani was arrested by the CBI on Tuesday in connection with the $1.77-billion fraud.