National Australia Bank has been dragged into a potentially damaging criminal case involving allegations of bribery and corruption against a former senior staff member and an external supplier of services to the bank.The allegations started to fly after police raids on two business premises and a private home.The action this week is the next stage in a process that started earlier this year, when detectives from the NSW State Crime Command's Financial Crimes Squad established Strike Force Napthali to investigate allegations of corrupt commissions being paid for contracts.Investigators had been told about a scheme whereby a person would allegedly receive corrupt commissions to authorise payments by a financial institution of invoices for a contractor, which were in excess of the agreed value of the contract. It seems at least one of those targets of the fake invoices was NAB, and the supplier of services has been named by News Ltd and Fairfax outfits as Helen Rosamond, director of executive projects and events company Human Group. This operation has supplied millions of dollars in training - including executive and board level training - to NAB over many years.If what is being alleged is true, Human Group's inside contact, someone with authority to clear the overinflated invoices, was alleged to have been former NAB chief of staff Rosemary Rogers, said to have been outed by a whistleblower.Upon hearing of the raids NAB chief executive officer, Andrew Thorburn, was forced to advise his senior leaders:"I want to let you know that, this morning, NSW Police informed us of the execution of a search warrant involving a former supplier of the bank.""This matter has been investigated by us, and was reported quickly to Police, and we will continue to fully cooperate with them. The people under investigation no longer work with the bank, or are involved with us."There are no customers involved or impacted," Thorburn said.South Wales Police confirmed that, "as part of ongoing investigations, Strike Force Napthali detectives executed three search warrants at businesses at North Sydney and Milsons Point, and a home at Potts Point…" These raids were carried out just after 9am yesterday morning (10 April)."Police investigators seized large amounts of documents and electronic storage devices, which will be examined by the squad's forensic accountants," the police statement continued.As would be expected in this situation, police and other authorities will be tracing assets and other indications of unexplained wealth.Financial Crimes Squad Commander, detective superintendent Linda Howlett, said the detectives on her Corporate Corruption Team were working closely with the bank's investigators "to track payments and other funds to determine if an offence has been committed."She added that this type of investigation "is complex and often protracted" and further information is needed: "we know there are people who have significant information that may assist us, and we are appealing for them to come forward."The allegations come at a time when NAB is still dealing with the fallout from its royal commission admissions that managers of several Sydney branches took bribes in exchange