Wall Street Values - business ethics and the global financial crisis by Michael A. Santoro and Ronaldo J. Strauss

Wall Street's business model transformed from serving clients and customers to earn commissions to mostly doing proprietary trading to trade directly in the market for profit. (happened in late 1970s when Wall Street firms became the issuers of debt securities, packaging and selling CMOs and other kinds of CDOs based on credit card debt and automobile financing.
Government deregulation and negligence, blurred the line between investment banks and commercial banks, lack of standard of capital ratio and supervision over operation. Government failed to take action when there were early signs of problems before crisis. 
Wall Street betting against its counterparties using deceiving methods, obscure information. Goldman Sachs in 2007 made billions of dollars whereas the counterparities it did business with lost billions. It had the most profitable year in its history just as the global economy was heading into a tailspin.