Federal regulators are offering a preliminary explanation of what happened May 6 when stocks plunged in value then made up ground before financial markets closed. Besides heightened volatility that day due to fears surrounding the European debt crisis, about half a dozen theories have been formulated by the Commodity Futures Trading Commission (CFTC) and the Securities and Exchange Commission (SEC) as to what happened to force the market down about 1,000 then back up again.

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http://thehill.com/blogs/on-the-mone...r-market-crash