2 million suspicious activity reports,or SARs, are filed by banks every year. Those reports are sent to the U.S. Treasury's Financial Crimes Enforcement Network (FinCEN), which has the job of determining whether the reports are evidence of criminal activity, and whether that activity should be investigated and punished.

The catch: FinCEN only has 270 employees, which means that FinCEN is dealing with a ratio of roughly 150 reports per employee per week. So it comes as little surprise to learn that most of the reports go unread, and the activity in them unpunished.

• That's a massive job: It can take a team of investigators weeks or months to investigate a single report.

For the record: A tiny subset of FinCEN reports — 2,100 in all — was leaked to BuzzFeed News two years ago. That kicked off a major international investigation, involving more than 400 journalists in 88 countries. After 16 months of work, their findings are now public.

• The journalists didn't have all the tools of law enforcement at their disposal, but they did have the luxury of being able to spend as much time as they wanted on one small group of reports.
• What they found was more or less what you'd expect: Some of those reports detailed what looks to be criminal activity by criminals. That's why they were marked suspicious by the banks.
• Journalists can't prove that any behavior was criminal. But it does seem with hindsight that banks allowed a lot of illegal money laundering to continue.

Between the lines: We don't know how much of that activity was caught or investigated by law enforcement. But it's a safe bet that it wasn't enough.

• We do know that the banks seem to have been generally happy to continue working with their customers after filing the SARs.
• All too often the banks file their SARs long after the criminals have moved on. The main reason for doing so is just that it's almost impossible to prosecute a bank for abetting money laundering if it has filed a SAR on the activity in question.

The bottom line: Banks need to be an integral part of the fight against money laundering, rather than simply filing SARs to protect themselves. The entire system needs a massive technological and financial upgrade — and law enforcement needs to grow more teeth, especially when it comes to prosecuting banks.

• My thought bubble: Money laundering persists because banks make more money when it exists than when it doesn't. The only effective way to fight it is to ensure that's no longer the case.