“What happened is the head diligence manager started yelling at his team, berating them, making them do reports over and over, keeping them late at night,” Ms Fleischmann said.

Another time, Ms Fleischmann said she approached a managing director named Greg Boester and warned he would be committing fraud if he sold the high-risk loans as low-risk securities but was again ignored.

A letter she wrote to another managing director, William Buell, about the consequences of reselling the bad loans as securities was nicknamed “The Howler” after the screaming letter from the Harry Potter novels.

“It used to be if you wrote a memo, they had to stop, because now there’s proof that they knew what they were doing,” Ms Fleischmann said. “But when the Justice Department doesn’t do anything, that stops being a deterrent. I just didn’t know that at the time.”

In 2008, she was dismissed from the firm in layoffs. In 2012, she started working with US prosecutors who were investigating JPMorgan.

Fleischmann was at a mall when she saw a Wall Street Journal headline on her iPhone: “JPMorgan Insider Helps U.S. in Probe”. Until that moment, Ms Fleischmann said, she had no idea how central she was to the government’s case.

“The stress started to build after I saw that news,” she says. “Especially as I waited to see if my name would come out and I watched my job possibilities evaporate.”

According to the Rolling Stone report, Fleischmann’s testimony was used to extract a $9 billion civil settlement with the bank.

Fleischmann said she now wanted to speak out.

“My closest family and friends don’t know what I’ve been living with,” she said. “Even my brother will only find out for the first time when he sees this interview.”

“I could be sued into bankruptcy,” she said. “I could lose my licence to practice law. I could lose everything. But if we don’t start speaking up, then this really is all we’re going to get: the biggest financial cover-up in history.”