Why are Issue Managers and Auditors not held accountable for S-chip frauds?

Dear Forummers,
Over the past weeks, I was going through the IPO prospectus and annual results of those S-chips fraud companies to see if I can spot trends in how they "massage" the accounts. It has been a tedious task but definately worth the experience.
 
I come to realise the fact that the frauds discovered by the "special audit team" post-frauds can actually be uncovered by an experienced corporate finance and audit professionals.
 
In the case of Hongwei, if the auditors can send more time to dig about their purchase of land and machinery, the Company may not even pass the due diligence test.
While the investors and public scolded the Chinese companies and their management, I also like to ask the questions, should these Singapore professionals be accountable for the poor due diligence conducted?
Can investors sue these professional parties for their negligence based on the law of negligence?
 

Macgyver, do u mind if you share some of your finding? What are the potential red flags and what should one look out for?