What caused market 'flash crash'?

A single large sale touched off the truly scary 600-point plunge in the Dow back in May, according to a long-awaited report by federal regulators. You'll probably need a degree in finance to figure it all out, but at least the findings put to rest some of the wacko theories that had popped up in the hours after the the session. From the NYT:

At about 2.32 p.m., a mutual fund -- which was not identified in the report, but which officials have identified as Waddell & Reed Financial of Kansas -- started a program to sell 75,000 E-Mini S.&P. 500 futures contracts, using computer algorithms. Normally, a sale of this size would take place over as many as five hours, but the large sale was executed in 20 minutes, the regulators said. The algorithm was programmed to execute the trade "without regard to price or time," the report said. The selling pressure was then transferred from the futures markets to the stock market, leading to the abrupt drop in individual stocks. Stock and stock-index futures prices were already declining on May 6 when, about 2:42 p.m., they suddenly plunged by more than 5 percent over the next five minutes.

Here's a copy of the report.