Regulators probing the stock market “flash crash” in May still have not uncovered a single cause but will point to “stub quotes” and other previously identified issues as having exacerbated the market’s dramatic drop, according to two sources familiar with the probe.

A third source said the Securities and Exchange Commission is still asking about a “smoking gun” that might explain the May 6 crash, when the Dow Jones industrial average plunged some 700 points before sharply recovering, all in about 20 minutes. Get the full story »