Joseph Cotchett, the San Francisco trial lawyer who last week made a splash when he sat down with convicted Ponzi schemer Bernie Madoff, is using the fruits of that interview to take aim at Wall Street, The Post has learned.

Since emerging from his 4½-hour sit-down with Madoff at a federal prison in Butner, NC, where the fallen financier is serving a 150-year sentence, Cotchett and his legal team have been furiously amending their lawsuits to name new defendants.

Among those new targets may be big financial firms, sources close to the legal team told The Post.

Cotchett and his army of lawyers “are investigating the investment banks — the people who had knowledge that this wasn’t a good investment, so to speak,” said a person familiar with the litigator’s plan.

“If they had done the due diligence, the fraud could have been caught. I think those that had the responsibility to do the due diligence didn’t do what they should have done.”

A likely target could be JPMorgan Chase, which has been accused of pulling its money from Madoff ahead of the breaking scandal, leaving its clients behind.

JPMorgan gave its clients access to Madoff through a product that let them lever their returns on funds that invested with the fraudster.

The bank invested $250 million of its own money in the product, known as levered notes, but pulled out months before Madoff was arrested in December.

A lawsuit filed in April by a Madoff investor claims JPMorgan Chase “unequivocally knew that Madoff’s investment returns were false” as far back as September 2008.

A JPMorgan spokesman declined to comment, citing the lack of a formal complaint against the firm.

The bank has previously cited “a wide-ranging review” of the firm’s overall hedge-fund exposure, as well as concerns about “the lack of transparency” as reasons it pulled its money from Madoff investments last year.

Cotchett declined to comment on which firms he may be going after, but suggested the list of victims’ claims offers some clues, as it names investment banking executives.

“If you have executives . . . investing in Madoff, you might want to see what their hedge funds are controlling,” he said, in an effort to offer a clue to his thinking.

Indeed, while the list of victims’ claims filed with Madoff trustee Irving Picard aren’t publicly available, JPMorgan shows up several times on a list of thousands of Madoff clients that emerged several months ago.

kaja.whitehouse@nypost.com