Billions in stolen crypto. Oligarchs' illicit assets. Financial crime is more complex than ever — and investigators say they need help to keep up

In its more than 100-year history, the IRS criminal investigation unit has helped put away the likes of Al Capone and John Gotti. It is the nation's sixth-largest federal law enforcement agency and the only one authorized to investigate federal criminal tax violations and pursue related financial crimes, such as money laundering, currency violations and terrorist financing.

But as the financial world grows more complex, so has criminal activity – and the unit tasked with bringing such illicit action to heel is facing an increasing challenge. About 75% of the unit's time is spent on tax investigations, but in recent years, they've shifted resources to emerging areas – like cryptocurrency. 

"Gone are the simple days of a person sending a transaction through a single bank account. That was easy to uncover: gain records from the bank. Now it's a very complicated web of sophisticated criminals trying to move money globally, "said Jarod Koopman from the IRS criminal investigation unit.