An IRS expert may arrive at trial with detailed spreadsheets, years of experience, and an explanation of why your tax returns do not match your financial records. That testimony can carry considerable weight with a jury.
But explaining the numbers and declaring that you knowingly violated the tax law are different matters.
In a federal criminal tax trial, an expert cannot give an opinion about whether you possessed the mental state that constitutes an element of the charged offense or a defense. Federal Rule of Evidence 704(b) reserves that determination for the jury. However, the rule does not exclude every expert opinion that could help prosecutors establish intent.
That distinction can shape your defense. An objection to an improper opinion may matter, but so can identifying the flawed assumptions, missing records, or unreliable calculations supporting otherwise admissible testimony.
At the Tax Law Offices of David W. Klasing, our dual-licensed tax attorneys and CPAs can examine both the government’s financial analysis and the legal limits on its proposed expert testimony. If prosecutors intend to use an IRS expert against you, obtain a defense assessment before assuming that the expert’s conclusions settle your case.
The Jury Must Decide Whether You Acted Willfully
For federal tax crimes requiring willfulness, the government must establish more than an incorrect return or an unfavorable accounting adjustment. In Cheek v. United States, the Supreme Court explained that willfulness requires a voluntary, intentional violation of a known legal duty. A genuine misunderstanding of that duty can negate willfulness, although disagreement with the law’s validity does not provide the same defense.
An expert may help jurors understand financial records and tax computations. The expert cannot simply supply an opinion that you possessed the criminal intent the government must prove.
A tax prosecution illustrates the boundary. In United States v. Windfelder, an IRS agent testified that the defendant “intentionally understated his income” and knew what had happened to assets involved in the case. The Seventh Circuit concluded that those opinions violated Rule 704(b) because they addressed the defendant’s knowledge or willfulness, elements of the charged crimes.
The court nevertheless upheld the conviction. It found the error harmless because the other evidence of willfulness was overwhelming. An improper expert statement therefore does not automatically lead to dismissal, acquittal, or a new trial. The defense must challenge the government’s underlying evidence as well as improper testimony.
This also explains why proving that an expert calculated the correct tax does not necessarily resolve the entire criminal case. The amount due and your knowledge of the relevant legal duty present different questions. Counsel must examine the evidence supporting each required element.
Why Some Testimony Bearing on Intent Can Still Reach the Jury
The Supreme Court clarified an important limit on Rule 704(b) in its June 2024 decision in Diaz v. United States.
The case involved a drug prosecution in which a government expert testified that most couriers know they are transporting drugs. The Court held that testimony about the mental state of most people in a group did not constitute an opinion about the defendant’s own mental state. It therefore did not violate Rule 704(b).
Although Diaz involved drug trafficking, its interpretation of the federal evidence rule matters in criminal tax trials. Prosecutors may seek to introduce generalized testimony that supports an inference about intent without directly asking an expert whether the defendant acted willfully.
That does not make every generalization about taxpayers, business owners, or tax preparers admissible. Counsel should examine whether the proposed testimony actually fits the case and satisfies the other evidence rules. Describing an opinion as a “general pattern” does not establish its reliability or usefulness.
For example, if an expert proposes to describe how people typically conceal business receipts, the defense should investigate the basis for that claim and whether the defendant’s actual records support the comparison. The jury must still evaluate the individual defendant’s conduct and state of mind.
Rule 704(b) also applies to defense experts. Your accountant cannot bypass the rule by announcing that you lacked the required criminal intent. A properly supported defense opinion may instead explain accounting practices, identify errors in the government’s analysis, or address other matters from which the jury can draw its own conclusions.
An IRS Title Does Not Establish a Reliable Opinion
An expert’s experience matters, but credentials alone do not satisfy Federal Rule of Evidence 702.
Under the current rule, the party offering expert testimony must show the judge that the testimony meets the rule’s admissibility requirements more likely than not. Those requirements include sufficient facts or data, reliable principles and methods, and a reliable application of those methods to the case. The testimony must also help the jury understand the evidence or determine a relevant fact.
That preliminary admissibility standard does not reduce the government’s separate obligation to prove the charged crime beyond a reasonable doubt.
For a criminal tax defendant, challenging reliability requires attention to the financial details. Suppose an analysis treats transfers between your own bank accounts as new business receipts. Or suppose the expert attributes income to the wrong taxpayer, counts the same transaction twice, or relies on incomplete records. Those problems may undermine the calculation and the broader conclusions prosecutors want the jury to draw.
Counsel must determine whether a particular defect supports excluding or limiting the opinion, challenging it through cross-examination, or both. Not every disagreement between accountants requires exclusion.
Rule 403 provides another potential basis for an objection. A court may exclude relevant evidence when its probative value is substantially outweighed by the risk of unfair prejudice, confusion, or misleading the jury. Evidence does not become unfairly prejudicial merely because it damages the defense. The objection must address the actual risk of an improper or misleading use.
Counsel should also distinguish an IRS witness’s factual testimony from expert opinions. An investigator may recount admissible observations or statements without serving as an expert on every subject. Conversely, the government cannot avoid the rules governing specialized opinions simply by labeling them ordinary lay testimony. Rule 701 excludes opinions based on specialized knowledge from its lay-witness provisions.
Build the Challenge Before the Expert Takes the Stand
Effective preparation begins with identifying exactly what the government intends its expert to say.
At the defendant’s request, Federal Rule of Criminal Procedure 16 requires written disclosures for specified government expert testimony. These include a complete statement of the opinions, their bases and reasons, the witness’s qualifications, and specified information about publications and previous expert testimony.
Those disclosures allow counsel to compare the proposed opinions with the underlying financial records. They can also reveal when an expert plans to move beyond a tax computation into an unsupported conclusion about the defendant’s knowledge.
A defense should address the particular opinions and evidence at issue. Counsel can seek appropriate pretrial rulings, challenge unreliable methods, identify testimony that crosses Rule 704(b)’s boundary, and prepare focused cross-examination. When the facts warrant it, a separate qualified expert can help test the government’s analysis or present admissible defense testimony.
The review should also examine contemporaneous evidence of what you knew and did. Records showing what you supplied to your preparer, questions you asked about reporting obligations, or instructions you gave your accounting staff may matter. Their significance depends on the complete record. Hiring a preparer does not automatically establish good faith or excuse knowing participation in a false return.
If the court admits the government’s opinion, counsel must remain prepared to challenge its assumptions and explain its limitations to the jury. If a witness exceeds the permitted scope, a timely, specific objection can help the court address the issue and preserve it for review.
A criminal tax conviction can bring imprisonment, financial consequences, and lasting damage to your professional standing. Assessing the strength of the expert evidence should form part of an informed defense strategy, including any decision about plea negotiations or trial.
Contact the Tax Law Offices of David W. Klasing if You Face IRS Expert Testimony in a Criminal Tax Case
Our dual-licensed tax attorneys and CPAs can evaluate the government’s proposed testimony alongside the accounting evidence that supports it. We can examine bank-deposit analyses, income reconstructions, tax computations, and preparer records to identify unsupported assumptions, omitted information, and evidence relevant to your knowledge and intent. Our combined legal and accounting experience helps us connect financial discrepancies with the elements prosecutors must prove.
We can review expert disclosures, develop appropriate evidentiary challenges, prepare cross-examination, and coordinate with qualified independent experts when necessary. Whether you face an investigation, an indictment, or an approaching trial, we can assess how the expert evidence affects your defense and available options. We can also work with existing defense counsel when the case requires focused criminal tax and accounting analysis.
Call the Tax Law Offices of David W. Klasing at (800) 681-1295 to schedule a confidential consultation. Bring any indictment, expert disclosure, IRS computation, or related financial records you lawfully possess. Before making decisions based on an IRS expert’s conclusions, have counsel examine what the evidence actually establishes and what the law permits that witness to tell the jury.
