Counsel assisting the Royal Commission into Misconduct in the Banking, Superannuation and Financial Services Industry, Rowena Orr, spent the greater part of yesterday afternoon building a case against NAB for failing to make a timely disclosure to ASIC after uncovering serious internal fraud at several branches.The crucial point put to Anthony Waldron, NAB's executive general manager for broker partnerships, was that the bank didn't start investigating likely misconduct among its home lending staff until October 2015. That was one month after a second internal whistleblower had exposed corrupt practices across at least five NAB branches in Greater Western Sydney, and five months after an earlier whistleblower reported that staff were misusing NAB's "Introducer program" for personal gain.Waldron disagreed: "We would already have been investigating; we wouldn't have waited until a second whistleblower [came forward]," he said.Orr countered: "That's not what you said in your witness statement."She read out an excerpt: "In October 2015, following these [two] anonymous calls, NAB's forensics services team conducted an investigation in relation to the allegations."Waldron countered with: "I guess what I was trying to say was that generally when we get a whistleblower report, we do work to look into it. Once the second whistleblower report has occurred, we would have expanded to a full-blown investigation...."This prompted an irascible interjection - one of several similar warnings - from Commissioner Kenneth Hayne: "There is a world of difference between 'would have' and 'I know' ... confine yourself to what you know, and what you can point to in your evidence ..."Orr then pointed to a letter NAB sent to ASIC in December 2015: "In late October 2015, an internal fraud investigation was initiated.  ... Is there any document you can point to that shows an investigation was commenced before October 2015?"Waldron "No".Orr: "You tell us in your statement that in October 2015 NAB convened a credit investigation working group, as well. ... And on 9 November 2015 NAB dismissed its first banker in connection with these allegations.  Is that right?"  Waldron: "Yes, that is correct."Orr then laid bare to the witness and to the Commission the unravelling of the network of kickbacks and irresponsible lending practices - often based on falsified documents - that was discovered.As November 2015 wore on, four more bankers were dismissed for a range of unacceptable conduct - for instance "falsely allocating multiple referrals to a particular introducer, despite that introducer not having referred the customers, resulted in the introducer receiving significant commission payments to which he had no entitlements." Some bankers who were dismissed shared in some of those commissions; others were dismissed for accepting fraudulent documentation or turning a blind eye to staff who did so.At about this time, NAB's group chief risk officer recommended creating a task force to look into the problems being uncovered.   "NAB knew that this pointed to significant failings in its risk management systems ... But by this time, November 2015, there had not been any report to the NAB board about any of this,