Castigate the regulators
To me there are clearly none more responsible for the current calamities than the regulators that thought up the crazy idea that it is possible to drive risks out of banking forcing the banks to heed the specific opinions of the credit rating agencies and without creating even larger systemic risk.
These regulators though they perhaps should not be sent to jail, should at least be named, shamed and fired… otherwise all talk of accountability is just a farce. If an impossible construction is contracted out who is really guilty when the construction falls?