NASDAQ CEO: 'Confluence of factors' caused market swoon

NASDAQ CEO Robert Greifeld on Friday said several factors contributed to yesterday's near 1,000 point drop in the Dow.

"I think it was a confluence of factors led by the marcro-economic environment, the futures market and then the listed market for those stocks," he told ABC's Good Morning America. 

Regulators originally thought a trading glitch caused the market to freefall, but Greifeld believes that it was only one aspect. The fear that financial unrest in Greece could be spreading to other European countries, and heightened activity in the futures market that spilled into the equity market also contributed to the issue.

During yesterday's chaos, several stocks quickly lost nearly all of their value. Accenture PLC was reduced to a penny, from $40 a share, and Proctor & Gamble stock lost 35 percent of its value in 2 minutes.

Greifeld said many of the trades that occurred during the crisis would be reversed. 

"For those trades that are cancelled, it is as if they did not happen," he said.