About a decade ago, Goldman Sachs’s due diligence for a residential mortgage-backed security showed an “unusually high” percentage of loans with credit and compliance defects. When a review committee asked “How do we know that we caught everything?” an employee said, “we don’t.” The committee approved the deal.

That exchange, and several other details on how Goldman packaged and sold securities backed by mortgages before the credit and financial crisis culminating in 2008, were unveiled on April 11 in a final settlement between the Wall Street bank and the Justice Department in which Goldman agreed to pay $5 billion.