In September 2008, the collapse of Lehman Brothers set off a full-blown financial panic.

NPR: Transcripts Show Fed Underestimated Crisis In 2007

In September of 2008 what had been a fairly gradual tightening of credit, became a panic tightening with the failure of Lehman Brothers.

FORBES: Nobel Laureate Paul Krugman is Correct, Cato Institute's Mitchell is Wrong