Two years after the subprime mortgage lending bubble started to pop with the collapse of Bear Stearns, politicians still want to know who to blame. They are making slow progress.

Last week, the Financial Crisis Inquiry Commission was told by Chuck Prince, former chief executive of Citigroup, that “everyone” from banks to rating agencies and regulators thought that triple-A tranches of collateralised debt obligations were safe investments, and that all were flabbergasted when the values collapsed.

This week, a Senate committee grilled Kerry Killinger, the former chief executive of Washington Mutual, one of the biggest mortgage lenders before regulators seized and sold it to JPMorgan Chase in September 2008. He insisted that WaMu's foray into subprime, spurred by Wall Street and by