Perhaps the largest problem for investors who might otherwise be willing to return to the mortgage market is the lack of transparency in privately issued securities. Investors interested in mortgage instruments are not allowed to analyze the loans going into these pools before they buy them.

The banks putting together the deals typically provide some data, like borrowers’ incomes and credit scores, as well as whether the loans backed primary residences or second homes. But investors don’t get access to actual loan files that can tell them what they need to know about the quality and types of the mortgages packed inside the deals.

A CIVIL case filed by the Justice Department last week against Bank of America highlights the downside of nondisclosure. In that matter, prosecutors accused the bank of misleading investors when it sold them a mortgage security in early 2008. Although the bank contended in marketing materials that the security contained prime loans that met its underwriting standards, more than 40 percent of those loans did not comply with those standards, prosecutors said.

Lawrence Grayson, a Bank of America spokesman, said the bank was fighting the case.

“These were prime mortgages sold to sophisticated investors who had ample access to the underlying data and we will demonstrate that,” he said in a statement last week.

But the Justice Department contends that the bank failed to disclose important facts to investors about the quality of the mortgages in the $850 million pool, which wound up performing badly. As of June 2013, prosecutors said, 15.4 percent of those mortgages had defaulted, indicating that they were of a far lower quality than advertised. The Justice Department estimates that investors will lose more than $100 million on the deal.

Then there’s another issue. Investors are also unlikely to take an interest in mortgage securities because serious conflicts of interest are still embedded in the process.

For example, in the aftermath of the crisis, investors learned that they could not rely on the trustee banks charged with overseeing these loan pools to do their jobs. The trustees are supposed to make sure that firms administering the loans treat investors fairly. These duties include taking in and distributing payments as well as foreclosing on borrowers.