看这两篇。

https://www.economist.com/blogs/economist-explains/2013/05/economist-explains-why-few-bankers-gone-to-jail

https://www.nytimes.com/2014/05/04/magazine/only-one-top-banker-jail-financial-crisis.html

上一篇简短易懂。第二篇很长，但摘抄一段：

“Federal prosecutors have their own explanation for how only one Wall Street executive landed in jail in the wake of the financial crisis. The cases were complex to investigate and would have been infernally difficult to explain to juries, some told me. Much of the crisis and banker transgressions stemmed from recklessness, not criminality. They also suggest that deferred prosecutions — with their billions in settlements and additional oversights — can be stricter punishments than indictments. Still, while the Department of Justice has not been without its successes — it won a guilty plea from BP in the Deepwater Horizon spill, and it’s currently going after traders in the wake of the  JPMorgan Chase  London Whale trading loss — these remain exceptions even beyond the financial sector. Federal prosecutors almost never bring criminal charges against top executives of large corporations, from banking to  pharmaceuticals  to technology. In March, the Justice Department entered into a deferred prosecution against  Toyota  but did not indict the company or any top executives.”

就是说，recklessness虽然后果很严重，但未必是，也未必能被证明criminality。次贷危机里，大多数大银行里，政府连下层操作人员都没法证明有criminality，如何去indict上层。那家小银行，喽啰们已经有罪了，起诉了上层，上层照样被判无罪。也正好从另一个角度看得出这类案件判刑事罪的难度。