It shows that he probably engineered it on purpose!

If you want to sleep tonight, Don’t Read It!

“In contradiction to the prevalent view of the time, that money and monetary policy played at most a purely passive role in the Depression, Friedman and Schwartz argued that “the [economic] contraction is in fact a tragic testimonial to the importance of monetary forces” (Friedman and Schwartz, 1963, p. 300).
…..

Of course, the stock market crash only worsened the economic situation, hurting consumer and business confidence and contributing to a still deeper downturn in 1930.”

Governor Ben S. Bernanke
Money, Gold, and the Great Depression.
At the H. Parker Willis Lecture in Economic Policy, Washington and Lee University,
Lexington, Virginia.
March 2nd, 2004

You can read also: Preparing for the Crash, The Age of Turbulence Update: 22/07/09., which tries to accomplish Greenspan Mission Impossible:

That is mission impossible. Indeed, the international financial community has made numerous efforts in recent years to establish such oversight, but none prevented or ameliorated the crisis that began last summer. Much as we might wish otherwise, policy makers cannot reliably anticipate financial or economic shocks or the consequences of economic imbalances. Financial crises are characterised by discontinuous breaks in market pricing the timing of which by definition must be unanticipated – if people see them coming, then the markets arbitrage them away.”

Alan Greenspan
The Age of Turbulence: Adventures in a New World [Economic Order?].

Plea for a New World Economic Order. explains the nature and causes of economic depressions and proposes a plausible alternative solution.