mumbai, March 20 -- Investors were left scratching their heads on Thursday after the abrupt resignation of HDFC Bank chairman Atanu Chakraborty the previous night, while shares of India's largest private sector lender plunged 5%. Despite the strong words from the exiting chairman, analysts do not expect any material irregularities at the bank, while attention turns to the reappointment of chief executive Sashidhar Jagdishan. An investor at the bank's conference call on Thursday morning summed up the exasperation: "So far, whatever I have heard on this call doesn't make me any wiser than I was an hour ago." Late on Wednesday, HDFC Bank released Chakraborty's resignation letter, in which he wrote of "happenings and practices within the bank" that were "not in congruence" with his personal values and ethics. At the morning call, HDFC Bank executives and board members assured investors that there were no material issues with the bank, insisting the board was not aware of why Chakraborty said what he said. HDFC Bank's interim chairman Keki Mistry, directors Sunita Maheshwari, Lily Vadera, Harsh Kumar Bhanwala, Renu Sud Karnad, and chief executive Jagdishan attended the call. Chief financial officer Srinivasan Vaidyanathan was also present. HDFC group veteran Mistry seemingly borrowed words from Chakraborty's statement to refute it. Mistry said he would not take on the responsibility of chairing the lender "if the systems, processes, governance practices in the bank did not align with my principles and my level of integrity." Mistry, 71, told reporters on a separate call that the bank management will speak to all major shareholders over the next one or two days to address their concerns. Jagdishan said every board member tried to persuade Chakraborty to stay back, or at least soften the language used in his resignation letter. As investors struggled to figure out whether to trust the former chairman's allegations or the new chairman's assurance, corporate governance experts demanded more accountability. "The board should constitute a committee of independent directors to look into the matter and put out a detailed statement to assuage investor concerns," said Shriram Subramanian, founder of proxy advisory firm InGovern Research Services. By making certain allegations, Chakraborty has done more harm than good to the investors, he said. "He should have explained in much more detail. The onus is on Chakraborty, as instead of writing those one or two lines in his resignation letter, he could have substantiated his allegations." The market did not take it well. Shares of HDFC Bank touched an intraday low of Rs.772 on the BSE, down 8.4%, before closing at 799.7 or 5.1% lower than Wednesday's close. The broader market was down 3.26%, with Sensex closing at 74,207.24. A couple of hours after the investor call, the Reserve Bank of India stepped in with reassurance. It said that on the basis of periodical assessments, there are no material concerns on record concerning HDFC Bank's conduct or governance. J.N. Gupta, managing director of proxy advisory firm Stakeholders Empowerment Services, said that if Chakraborty were a simple director, he could have said that the chairman was not listening to him, his dissent was not recorded. However, that was not the case....