the person has been laundering money for years.
In general if you don't file a tax return there is no statute of limitations. For some hidden financial crimes the statute of limitations only begins from the date of discovery rather than the date the act is committed. If the behavior is still ongoing this would also mean that charges can still be filed.
These statements do not constitute legal advice. They are meant to be general in nature, for any specific legal questions you should always seek the counsel of an experienced attorney.
Under Washington State law, money laundering is a Class B Felony. Since it is covered under RCW 9A.83, the Statute of Limitations would be six years from commission or discovery, whichever is later. There are several different types of tax fraud, both state and federal, for businesses and individuals. More information would be needed, but the best way for you to get answers would be to have a free consultation with one of the many great attorneys who do criminal defense in Seattle - preferably one who deals with tax issues as well.
The other attorneys have answered your question very well. I will simply agree that the statute of limitations starts running from either the time the crime is committed or when it is discovered. If the crime is still going on, the statute of limitations has not begun running.