When hedge funds own a lot of the float (like in JEC) this can happen. Their partners want their money back now, so they are forced to sell all their shares. Other hedge funds know this so they massively short sell the stock, forcing others to sell at lower and lower prices. Its called blood in the water, and if you don't understand read Cramer's "Confessions of a Street Addict" when he went through a hedge fund redemption and you'll find out.
Joe: good points. but trading at a forward p/e of 10? That has never happened to JEC ever. I still say it is an extremely good buy at this level. Opening offices in India and the Mideast is a very smart move as the infrastructure demands there are huge.