The causes of the 1929 stock market crash have been shrouded in mystery for more than 60 years, but new research by a UC Davis economist may help solve this riddle. George Bittlingmayer, currently visiting the University of Chicago for a year, has identified what he calls the "smoking gun" -- a radical shift in the 1929 government's policy toward business. President Herbert Hoover's attorney general repudiated the antitrust policy practiced under President Calvin Coolidge and announced stricter enforcement of the antitrust laws just days before the Oct. 29, 1929, stock market crash. The attorney general's October 1929 announcement fell in the middle of a one-week slide of 30 percent in the Dow Industrial average. By itself, the timing of the crash might be a coincidence, but other periods also show a close link between saber rattling by antitrust authorities and stock crashes, says Bittlingmayer. He also cautions that we may be drawing the wrong lessons from stock crashes when we attribute them to speculative excesses. The stock market also can change dramatically in response to governmental action. Given the broad discretion of the president and other officials responsible for the enforcement of the laws governing business, modern day bursts of anti-business policy cannot be ruled out, says Bittlingmayer.