How should the U.S. government deal with a foreign bank that conspired to cheat the Treasury out of billions in revenues by helping rich American hide money overseas? Here's one idea: slap the bank with a big financial penalty, the costs of which will mainly be picked up by shareholders who had nothing to do with the crime while letting the culpable individual bank officers off the hook. That is what the U.S. did with Swiss bank UBS five years ago, after it was found to have aided tax evasion.

Or how about this idea: Treat a large-scale criminal conspiracy to abet tax evasion as, well, a crime -- one that's investigated by agents with badges and guns, gets tried in a criminal court (if defendants can be found or extradited), and where there's at least the possibility that somebody will go to jail.

That should have been the logical way to handle evidence that yet another Swiss bank, Credit Suisse, engaged in a massive effort to abet tax evasion by thousands of wealthy Americans. Such evidence began surfacing a few years ago, so by now you'd hope that the Feds would have done wiretaps, kicked down doors, pressured witnesses, made arrests, and issued extradition orders. Instead, though, all we have is a relatively minor SEC settlement with Credit Suisse and a big report by the Senate Permanent Subcommittee on Investigations, released yesterday, that documents Credit Suisse's criminality in exhaustive and colorful detail. As the Times summarizes it

The 176-page report charges that from at least 2001 through 2008, the Swiss bank helped its American customers evade taxes through a variety of means, including opening accounts in the name of shell companies and sending Swiss bankers to the United States to secretly recruit new clients and avoid creating a paper trail.

Seven years of criminal activity by a banking giant with a huge presence in the U.S., explicitly aimed at depriving the federal government of substantial tax revenues. Wow. In some countries, you could imagine that the ripped off government in question would raid and close all the bank offices within its borders.

Of course, this isn't the first time that this Senate subcommittee, chaired by Carl Levin, has revealed large-scale criminal activity by an international bank. We wrote here a while ago about Levin's huge investigation of HSBC, which revealed how that bank had helped drug cartels and rogue nations launder money, and access the U.S. banking system. Shocking revelations about clear-cut crimes, which led to -- yes, you guessed it -- a big financial penalty in which not a single bank executive was held responsible for anything.

I just don't get it. Why have the biggest investigations of criminality by international banks been led by staffers in the legislative branch? I'm glad the Department of Justice has gone after insider trading among hedge funds, but why is the government spending huge resources to learn whether greedheads got an edge over regular investors when major criminal banking conspiracies that cost us billions or empower our enemies get short shrift?

I know what the standard answer to these questions are: government prosecutors always go after the low-hanging fruit, where convictions are probable. But it's worth noting that Levin's new report offers a damning picture of passive federal authorities who could have cracked down earlier and harder.

In the face of congressional gridlock, President Obama has said he wants to use his executive powers to make a difference during his remaining time in office. Pushing federal investigators and prosecutors to get tougher with international banks is an obvious thing he could do. The authorities could start by following up on Levin's report on Credit Suisse.