We should keep in mind the role of the auditor as it relates to fraud. It is the auditors responsibility to design and perform an audit that will detect material misstatements whether due to error or fraud.
This responsibility requires auditors to exercise professional skepticism, which assumes neither honesty or dishonesty. Therefore, when management represents to the auditors that they are making an unbiased judgment call and then present sufficient evidence to support their judgment call – then the auditor can satisfy himself or herself that they have fulfilled their responsibility.
In the Toshiba case, the auditors were Ernst & Young. Eventually, they will need to answer the question: did you perform an audit in accordance with GAAS, with a specific focus on whether the audit was planned and performed to detect material misstatements due to fraud. The answer to that question will focus on what evidence was obtained and analyzed relating to the accounting for long term contracts and whether the auditors “should have” identified the fraud based on the management representations and other evidence they received.
The most likely scenario is that EY will settle with the Toshiba shareholders and the general public will never know whether the audits were done in accordance with GAAS or not. But always keep in mind, just because there is fraud in financial statements that are material – it is not a foregone conclusion that the auditors did not do their job.