Three sets of investigators handle tax fraud in the United States. At the federal level, IRS Criminal Investigation is the only agency authorized to investigate crimes under the Internal Revenue Code, and once it builds a case, prosecution moves to the Department of Justice’s Criminal Division, which absorbed all criminal tax proceedings from the former Tax Division in December 2025. State revenue agencies run their own investigations into state income tax, sales tax, and payroll tax violations, and they routinely share data with the IRS. Getting caught by one of these agencies often means hearing from the others.
IRS Criminal Investigation
IRS Criminal Investigation, usually written as IRS-CI, is the federal government’s dedicated financial crimes unit. About 2,100 special agents cover tax fraud, money laundering, and Bank Secrecy Act violations.1Internal Revenue Service. Criminal Investigation (CI) at a Glance No other federal law enforcement agency can investigate violations of the Internal Revenue Code. The FBI and DEA sometimes work money laundering cases, but when the offense sits inside the tax code, CI owns it.
Special agents carry the full authority of federal law enforcement officers under 26 U.S.C. § 7608. They execute search warrants, make arrests, and carry firearms.2Internal Revenue Service. IRS Internal Revenue Manual 9.1.2 Authority They can make warrantless arrests when a tax felony is committed in their presence or when they have reasonable grounds to believe one has been committed. The agency also maintains a federal conviction rate above 90 percent on the cases it brings.
CI has expanded heavily into digital asset enforcement in recent years. Through the Joint Chiefs of Global Tax Enforcement (J5), an international coalition, the agency issued advisory guidance in 2024 flagging cryptocurrency risk indicators for financial institutions, including layering techniques, darknet marketplace exposure, and transactions routed through jurisdictions with weak anti-money-laundering controls.3Internal Revenue Service. J5 Issues Notice to Financial Institutions About Risk Indicators Tied to Cryptocurrency Assets
How Tax Fraud Investigations Begin
Investigations rarely start with a raid. They start with information, and the information comes from a handful of predictable sources.
Whistleblowers
The IRS Whistleblower Office, established under 26 U.S.C. § 7623, pays informants for information that leads to the collection of unpaid taxes. When the tax in dispute exceeds $2 million (and, for individual targets, gross income exceeds $200,000 in the relevant year), the whistleblower gets a mandatory award of 15 to 30 percent of the collected proceeds.4Office of the Law Revision Counsel. 26 USC 7623 – Expenses of Detection of Underpayments and Fraud Smaller cases carry discretionary awards up to 15 percent, capped at $10 million. The program gives insiders at companies engaged in fraud a strong financial reason to talk.
Civil Audit Referrals
Many criminal tax cases begin as ordinary audits. IRS civil examiners are trained to recognize what the Internal Revenue Manual calls “badges of fraud,” and when they see them, the file shifts from civil to criminal.5Internal Revenue Service. IRS Internal Revenue Manual 25.1.2 Recognizing and Developing Fraud The indicators fall into rough categories: omitting entire sources of income, personal spending that dwarfs reported earnings, concealed bank accounts or crypto holdings, fictitious deductions, altered documents supporting refundable credits, multiple sets of books, and backdated or postdated records.
When a civil examiner identifies these signs, they document the findings and notify a group manager. If the evidence points to intentional fraud rather than carelessness, the examiner must suspend collection activity and refer the case to Criminal Investigation. That referral turns a civil matter into a criminal one, and the taxpayer usually has no idea the switch has happened.
How IRS-CI Builds a Case
When a taxpayer keeps clean books, proving unreported income is a straightforward comparison of records to returns. The harder cases involve records that are incomplete, hidden, or destroyed. For those, courts have approved several indirect methods that let agents reconstruct income from circumstantial evidence.6Internal Revenue Service. IRS Internal Revenue Manual 9.5.9 Methods of Proof
The net worth method calculates the change in total assets minus liabilities over a period, adjusts for personal spending and nontaxable items, and compares the result to reported income. If net worth jumped $400,000 in a year while the return showed $80,000, the gap needs an explanation. The bank deposits method totals deposits across every account, adds known cash expenditures, subtracts transfers and nontaxable deposits, and measures the result against reported income. The expenditures method works when net worth stays flat but the taxpayer is clearly living far beyond what the return suggests; agents tally actual spending and compare it to reported income. Luxury purchases, travel, and real estate improvements all become evidence.
These methods exist because tax cheats tend to destroy direct evidence. Juries find the math intuitive: if someone spent $300,000 but reported $60,000, something is wrong.
The Department of Justice Takes Over Prosecution
IRS-CI investigates, but it does not prosecute. That authority belongs to the Department of Justice. Until December 2025, a dedicated Tax Division handled all criminal and civil tax litigation. That division no longer exists. A Federal Register rule effective December 9, 2025, transferred all criminal tax proceedings to the DOJ’s Criminal Division and all civil tax litigation to the Civil Division.7Federal Register. Transfer of the Functions of the Tax Division to the Civil Division and the Criminal Division
After CI completes an investigation, the Special Agent-in-Charge refers the case to DOJ with a recommendation. Attorneys review the evidence and either authorize prosecution, authorize a grand jury investigation to gather more, or decline the case and return it to the IRS. Grand juries can compel witnesses to testify and produce documents through subpoenas, and the proceedings stay under seal.8Legal Information Institute. Federal Rules of Criminal Procedure Rule 6 – The Grand Jury Review runs through multiple levels of sign-off, and cases with significant policy implications climb to the Deputy Assistant Attorney General or higher.
Once a case is authorized, federal prosecutors in the relevant U.S. Attorney’s Office handle trial, plea negotiations, and sentencing. IRS special agents typically serve as the government’s key witnesses, walking juries through the financial evidence. Agents gather facts; prosecutors argue law. Neither controls the other.
The federal tax crimes that emerge from these referrals fall mostly under three statutes. Tax evasion under 26 U.S.C. § 7201 carries up to five years in prison and fines up to $100,000 for individuals or $500,000 for corporations.9Office of the Law Revision Counsel. 26 USC 7201 Attempt to Evade or Defeat Tax Filing a materially false return, or helping someone else do so, is a felony under 26 U.S.C. § 7206 with up to three years in prison and the same fine ceilings.10Office of the Law Revision Counsel. 26 US Code 7206 – Fraud and False Statements Willful failure to file under 26 U.S.C. § 7203 is a misdemeanor punishable by up to one year and a $25,000 fine for individuals.11Office of the Law Revision Counsel. 26 US Code 7203 – Willful Failure to File Return, Supply Information, or Pay Tax All three require the government to prove willfulness, not just error.
State Revenue Investigators
Federal agencies are not the only ones watching. Every state has its own taxing authority, and most maintain investigative units focused on state income tax, sales tax, and payroll tax violations. These units operate under their own statutes and penalty structures, and a state investigation can proceed entirely independently of anything happening at the federal level.
Common state-level targets include businesses that collect sales tax from customers but never remit it, individuals who claim false residency in a no-income-tax state to dodge their real home state’s taxes, and employers who pay workers off the books to avoid payroll taxes. Penalties range widely across states but can include prison time, restitution, and revocation of professional licenses for accountants, attorneys, and other regulated professionals.
Federal and state agencies share data through formal agreements. The IRS partners with state taxing authorities to exchange audit results, individual and business return information, and employment tax data.12Internal Revenue Service. State Information Sharing An IRS audit that uncovers unreported income will likely reach the state revenue department, and a state investigation flagging suspicious federal returns can generate a referral to CI. Joint task forces are common when a scheme crosses jurisdictional lines.
What the Government Can Still Reach
The criminal side has time limits. Under 26 U.S.C. § 6531, most tax crimes carry a three-year statute of limitations, and tax evasion, filing false returns, and willful failure to file get a six-year window, measured from the commission of the offense.13Office of the Law Revision Counsel. 26 US Code 6531 – Periods of Limitation on Criminal Prosecutions Time spent outside the United States or as a fugitive does not count.
The civil side is more aggressive. Under 26 U.S.C. § 6501, when a taxpayer files a false or fraudulent return with intent to evade, the IRS can assess additional tax at any time. There is no deadline.14Office of the Law Revision Counsel. 26 US Code 6501 – Limitations on Assessment and Collection The civil fraud penalty under 26 U.S.C. § 6663 adds 75 percent of the underpayment attributable to fraud on top of the tax owed, and once the IRS proves any portion was fraudulent, the whole underpayment is presumed fraudulent unless the taxpayer rebuts it by a preponderance of the evidence.15Office of the Law Revision Counsel. 26 US Code 6663 – Imposition of Fraud Penalty Even after the criminal window closes, civil exposure from a fraudulent return does not.
Taxpayers who have willfully failed to comply can limit criminal exposure through the IRS Voluntary Disclosure Practice, but only if they come forward before the IRS starts a civil exam, receives a third-party tip, or acquires information about the specific noncompliance through a criminal enforcement action.16Internal Revenue Service. IRS Criminal Investigation Voluntary Disclosure Practice Once the agency already knows, the door is closed. The program also excludes income from illegal sources, which for these purposes includes activity that is legal under state law but illegal federally, such as marijuana sales in some states.
If IRS-CI Contacts You
By the time IRS-CI special agents call or appear at the door, the investigation has usually been running for months. Agents rarely make contact until they have gathered substantial evidence. The right to remain silent and the right to an attorney only protect you if you invoke them. Say nothing beyond identifying yourself, and retain a criminal defense attorney experienced in federal tax matters before answering questions, producing documents, or signing anything. Special agents are trained investigators, and unguarded statements become evidence.