According to the Toronto Globe and Mail’s summary of the G20 conference statement:

…leaders blamed the crisis on investors seeking higher returns without adequately calculating the risks. A lack of transparent financial products and unsound management practices, along with regulators’ lack of appreciation of growing problems are also to blame. Although the United States was not named as the main culprit, the declaration did point the finger at “advanced countries.”

“These developments, together, contributed to excesses and ultimately resulted in severe market disruption.”