Watch The Untouchables on PBS. See more from FRONTLINE.

In "The Untouchables," Frontline investigates why Wall Street's leaders have escaped prosecution for any fraud related to the sale of bad mortgages. Are Wall Street's big bankers untouchable?

Producer Martin Smith joined HuffPo Live on Tuesday to discuss his investigation into the lack of prosecution of Wall Street executives for any fraud related to the sale of bad mortgages:

Commenting on clips from the episode showing former home loan underwriters explaining how they would laugh as they pushed through mortgages that were too expensive for the borrowers, Smith said this type of behavior was "very frequent and common."

"There are lawsuits that name 35 -- easily 36, 37 -- of these kind of testimonies," Smith told HuffPost Live host Jacob Soboroff. "And these guys are joking about it at this point, but of course it's not really funny in the end because it all resulted in the collapse of 2008, a million people losing their houses, many people out of work and businesses seeing demand sink."

"It was like a party," one former loan underwriter tells Frontline's" Martin Smith. "We were getting through these loans as quick as we can. They were not being looked at like they should've been looked at."

A full transcript of the report is available here.

Watch The Untouchables Preview on PBS. See more from FRONTLINE.

The PBS Frontline investigation "The Untouchables," airs on Tuesday, January 22, 2013. Frontline investigates how more than four years since the financial crisis, not one senior Wall Street executive has faced criminal prosecution for fraud. Are Wall Street executives “too big to jail"? Check out the preview video above. You can check your local viewing schedule here.