“This is the miracle of not having securities mapped to the underlying loans,” said Josh Rosner, a specialist in mortgage securities at Graham-Fisher, an independent research firm in New York. “There is no industry repository for mortgage loans. I have heard of instances where the same loan is in two or three pools.”

The process of putting together a mortgage pool begins when a home loan is originated by a bank or mortgage lender. That loan is typically sold to a Wall Street firm that pools it with thousands of others. Once a pool is packaged, it is sold to investors in different slices, based on risk. A trustee bank oversees the pool’s operations, ensuring that payments made by borrowers go to the appropriate investors.

Lawyers who represent troubled borrowers complain that trustees overseeing home loan pools often do not produce proof, usually in the form of a mortgage note, that their investors own a foreclosed property. And a recent study of 1,733 foreclosures by Katherine M. Porter, an associate professor of law at the University of Iowa, found that 40 percent of the creditors foreclosing on borrowers did not show proof of ownership. Such proof gives a creditor standing to foreclose against a borrower and is required by law.

“The big issue in all these cases, whether we are dealing with a bankruptcy court, a state court or a federal court, is who really owns the mortgage note, and that is allegedly what they securitized,” said O. Max Gardner III, a lawyer who represents borrowers in foreclosure in Shelby, N.C. “A collateral question is, has that mortgage note really been transferred and assigned to the securitization trust? If not, then they really don’t have standing. It’s Law School 101.”

When a loan goes into a securitization, the mortgage note is not sent to the trust. Instead it shows up as a data transfer with the physical note being kept at a separate document repository company. Such practices keep the process fast and cheap.

Because most foreclosures proceed without challenges from borrowers, few judges have forced trustees like Deutsche Bank and Bank of New York to prove ownership by producing a mortgage note in each case.

Borrower advocates cheered Judge Boyko’s ruling.

The plaintiff’s argument that “‘Judge, you just don’t understand how things work,’” the judge wrote, “reveals a condescending mindset and quasi-monopolistic system where financial institutions have traditionally controlled, and still control, the foreclosure process.” The cases could be filed again in state court, however.