The New York attorney general, Eric T. Schneiderman, has opened an investigation into the collection practices of the National Collegiate Student Loan Trusts, one of the nation’s largest owners of private student loan debt, according to Mr. Schneiderman’s office.

The attorney general’s office sent subpoenas on Wednesday asking for information on every collection lawsuit filed by National Collegiate’s trusts against New York residents.

National Collegiate’s trusts have aggressively pursued in court borrowers who fall behind on their student loan payments. An article this week in The New York Times drew attention to the trusts’ inability in many of those lawsuits to produce the paperwork needed to prove that the trusts own the debts they seek to collect. Judges around the country have dismissed dozens of cases filed by National Collegiate’s trusts because of flawed or missing paperwork.

The 800,000 private student loans that National Collegiate owns, totaling more than $12 billion, were originated a decade or more ago by other lenders, then packaged into securities and sold to investors. As the debt changed hands, crucial paperwork documenting the loans’ ownership appears to have been lost, according to court filings in a bitter legal fight among parties involved in operating the trusts.