WASHINGTON — As a doctoral candidate in physics at Princeton two decades ago, Gregg E. Berman spent a year and a half in a laboratory searching through subatomic data for an elusive particle called the heavy neutrino.

Now, from his small office at the Securities and Exchange Commission here, the former physicist is busy completing a similarly painstaking task, supervising a team of more than 20 investigators who have spent the last five months scrutinizing reams of stock-trading data and hundreds of interview transcripts in an effort to figure out why stock prices went into free fall for 20 terrifying minutes on May 6.

Their long-awaited report on the so-called flash crash, in partnership with the Commodity Futures Trading Commission, is due to be published in the next two weeks.

Mr. Berman, 44, will not say exactly what will be in the report, but he says that it will not simply restate what regulators have already said — that markets were volatile because of worries over the debt crisis in Europe, causing some computerized trading programs to stop trading, and finally causing computers on other exchanges to misread the pullback as a rapid bidding down of stock prices.