Wall Street Close: benchmarks tumble into manic quater's end

• Dow Jones unofficially closes down 439.70 points, or 1.97%, at 21,887.78.
• NASDAQ unofficially closes down 81.01 points, or 1.04%, at 7,693.14.
• S&P unofficially closes down 44.19 points, or 1.68%, at 2,582.46.

More to come...