State Bank of India (SBI) is looking at various ways to declare Vijay Mallya a willful defaulter and trying build a strong case in that regard, an SBI source has said to a news agency. The source said that as per RBI guidelines, it would have to be proven that the borrower had diverted funds which he taken from the bank and not paying up despite having the ability to pay.SBI alone has an exposure of Rs 1,600 crore to grounded airline Kingfishe. SBI leads a 17-member consortium of lenders that is trying to recover dues running into over Rs 7,500 crore in principal alone from Kingfisher Airlines.