No scandal in recent years has hung over the art market as heavily as the Knoedler & Company forgery case.

At its heart lies a mystery. Was Knoedler, the distinguished old gallery that sold more than 30 fake paintings said to be by Pollock, de Kooning and other titans of Abstract Expressionism, in on the scam? Or were the gallery and its longtime director, Ann Freedman, cruelly hoodwinked along with collectors who together paid around $63 million for the bogus works?

This week the puzzle may start to unravel: The first trial to arise from the sales, in a lawsuit involving the 2004 purchase of a fraudulent Rothko, is to open on Monday in United States District Court in Manhattan. A parade of witnesses from the art world are to testify, just possibly including Glafira Rosales, the former Long Island dealer who, for 15 years, consigned fakes to Knoedler, passing them off as masterworks from a mysterious collection based in Zurich and Mexico City.

All of them had actually been painted by a Chinese immigrant in Queens.

“It’s a unique opportunity for a public hearing of the machinations of the art world, which are usually very discreet,” said Nicholas M. O’Donnell, an art lawyer in Boston.