One of the many remarkable things about the massive leak of documents known as the Panama Papers is what's not there. Americans. The documents, related to a Panamanian law firm that specializes in creating shell companies for many of the world's richest people, provide a glimpse into how secret fortunes and ill-gotten gains are moved through a shady financial network, according to The International Consortium of Investigative Journalism, which worked with news organizations around the world to analyze the files. The clients and connections included current and former world leaders, famous athletes and billionaires, but also notorious underworld operatives. But nowhere among the bold-faced names are any that live in the United States. That doesn't necessarily mean that Americans are more upfront, or more law abiding, than their counterparts around the world, experts said. But there are a number of possible reasons why none have showed up in the coverage. First, this was a leak of more than 11 million documents, and it will take some time for the ICIJ to scour them. "So maybe there are revelations about specific Americans and secret funds that we haven't heard about," said Matt Gardner, executive director of The Institute on Taxation and Economic Policy, a research organization. RELATED: Iceland's Prime Minister David Gunlaugsson resigns At the same time, it's possible that Americans who do this sort of thing simply worked with law firms other than Mossack Fonseca. There are numerous other firms, large and small, American and foreign, that help wealthy clients set up offshore shell corporations — which isn't of itself illegal, as long as the clients aren't trying to hide criminal proceeds or dodge tax collectors, experts said. Mossack Fonseca co-founder Ramon Fonseca has said that his firm broke no laws, and that it wasn't responsible for how the corporations were used. "This firm is one of thousands in the world and there are hundreds or thousands just like it in the U.S.," said Ana Owens, a tax and budget advocate at U.S. Public Interest Research Group (PIRG), a federation of state-level consumer advocacy organizations. "If a company in the U.S. can do the exact thing for you as this company in Panama, then you might as well do it right here in the U.S. And its perfectly legal, which is the issue." She cited a series of stories by the Portland Business Journal last year that revealed federal authorities' failed attempts to catch a California-based "corporation mill" committing fraud, despite evidence of financial crimes by companies related to the firm. In January, the British activist group Global Witness found several New York real estate lawyers who expressed willingness to help an undercover reporter form shell companies to secretly move suspect money from Africa. The United States is a tax haven Two states, Delaware or Nevada, along with the U.S. Virgin Islands, are known in particular for loose regulations and low taxes, making them attractive for people to hide their activities and assets behind a corporate facade. The British-based Tax Justice Network released a "Financial Secrecy Index" of popular tax havens last fall that ranked the United States third, behind Switzerland and Hong Kong, and far higher than Panama, at 13th. What may keep more super-rich Americans from seeking tax havens is that they have less to lose, said Lee Sheppard, an expert in international finance at the nonprofit research organization Tax Analysts. "For Americans, taxes aren't all that high relative to other developed countries," Sheppard said. But that doesn't keep some from trying. Larry Langdon, a former IRS commissioner who now practices tax law, said many of America's biggest businesses, including Apple and Google, legally cut their tax burdens by forming companies in countries with even lower rates than the United States' — not only typical havens like islands in the Caribbean, but also job-hungry countries like Ireland. The IRS wants to catch Americans who are breaking the law by hiding assets. But that has become difficult as budget cuts have forced the IRS to prioritize large corporations over wealthy individuals, he said. RELATED: President Obama addresses massive Panama Papers leak Reform advocates say one possible solution lies in a bill pending in Congress called the Incorporation Transparency and Law Enforcement Assistance Act, which would require states to collect data on the "beneficial ownership" of shell companies. That information could be made available to investigators. U.S. PIRG is sending dozens of activists to Washington next week to try to push lawmakers to pass it, Owens said. If they get their way, advocates say, Americans would have fewer opportunities to hide assets. The absence of Americans on the Panama Papers doesn't minimize the broader problem, Gardner said. "This shouldn't just be a Panama story," he said. "This should be a wakeup call to us that some incredibly damaging things could be going on behind the scenes of these shell corporations." This story originally appeared on NBCNews.com.