Can a Lawyer Providing Counsel for a Criminal Defendant Also Serve as an Expert Witness at the Same Trial?

Answering a Paid Subscriber Question

Today, I am answering a question from a paid subscriber.

“Can you both be paid to provide legal counsel to the defendant and serve as an expert witness???”

Short Answer: While there is jurisdictional nuance, the answer is generally no.¹

There are a couple of issues that bar a criminal defendant from having his own defense attorneys testify as expert witnesses. First, almost every jurisdiction has what is known as the “advocate-witness” rule. That rule generally precludes an attorney who is representing a client from being a witness to a disputed fact in a trial where they are representing that same client.

Second, many jurisdictions have adopted a rule that the files of testifying experts are not confidential. It would therefore be unethical for an attorney to try to enter into that dual-role relationship as it would jeopardize client confidentiality.

I. Some Basics

In order to more fully answer this question, some basic rules related to the admission of evidence in trial should be laid out. Again, there are jurisdictional variations but these are the basic rules.

1. Only relevant evidence is admissible in a trial.² Evidence is relevant when it could reasonably prove or disprove a disputed fact that determines the case outcome.³ “Evidence is relevant if it tends “‘logically, naturally, and by reasonable inference’ to establish material facts such as identity, intent, or motive.”⁴

2. While there is a baseline assumption that all relevant evidence is admissible at trial, there are numerous laws that will prevent the admission of that evidence.⁵

3. The court can exclude otherwise relevant evidence when its value is outweighed by the likelihood that it will (1) unnecessarily waste time, (2) unduly prejudice the jury, confuse issues, or mislead the jury.⁶ This rule applies to expert witness.⁷

4. A witness generally cannot testify to something where they lack personal knowledge of the matter.⁸ A non-expert witness is generally only allowed to give opinion under two circumstances:

   1. The opinion is rationally based upon their personal perception.⁹

   2. The opinion helps the finder of fact understand their testimony.¹⁰

5. In a criminal trial, a criminal defendant has a fundamental constitutional right to a fair opportunity to present a defense.¹¹ This includes the right to put on witnesses in his or her defense.¹² However, basic rules of evidence are not unconstitutional and judges still have discretion to exclude evidence offered by criminal defendants.¹³

II. The Advocacy-Witness Rule

One of the issues with a criminal defendant having his defense attorneys testify as expert witnesses is the advocate-witness rule, which applies with special force in criminal trials.

In a criminal trial, a prosecutor is generally not allowed to be a witness.¹⁴ The rule appears to be universally applicable to defense attorneys as well.¹⁵ It is designed to protect the rights of criminal defendants and protect the integrity of the trial.¹⁶ This is known as the “advocate-witness rule”.¹⁷

As explained by the 9th Circuit Court of Appeals:

The advocate-witness rule prohibits an attorney from appearing as both a witness and an advocate in the same litigation. This venerable rule is a necessary corollary to the more fundamental tenet of our adversarial system that juries are to ground their decisions on the facts of a case and not on the integrity or credibility of the advocates. Accordingly, adherence to this time-honored rule is more than just an ethical obligation of individual counsel; enforcement of the rule is a matter of institutional concern implicating the basic foundations of our system of justice.¹⁸

Thus, attorneys have a choice. They can proceed either as the lawyer or as a witness and withdraw from being the lawyer.¹⁹

The American Bar Association Model Rules of Conduct, which have been adopted in California, provide that a lawyer shall not act as an advocate in a trial in which the lawyer is likely to be a witness except under limited exceptions.

Those exceptions are:

1. The lawyer testifies about something that isn’t contested by the parties.²⁰

2. The lawyer testifies about the nature and value of legal services they render in the case.²¹

3. The lawyer obtains the informed written consent of the client.²²

Does this mean that a criminal defendant can simply give informed written consent to having their attorney testify as an expert witness?

No. That’s because a trial court still has discretion to order the withdrawal of counsel when that lawyer would serve as a witness when the judge observes a conflict.²³

What the American Bar Association has explained in its commentary about the rule and creating its narrow exception is:

The prohibition against a lawyer serving as advocate and testifying as a witness in the same matter is essentially aimed at eliminating confusion over the lawyer’s role. This confusion could prejudice one or more of the parties or call into question the impartiality of the judicial process itself. As an advocate, the lawyer’s task is to present the client’s case and to test the evidence and arguments put forth by the opposing side. A witness, however, provides sworn testimony concerning facts about which he or she has personal knowledge or expertise. The very fact of a lawyer taking on both roles will affect the way in which a jury evaluates the lawyer’s testimony, the lawyer’s advocacy, and the fairness of the proceedings themselves.”²⁴

Now, in some contexts, there is a distinction between “opinion” and “fact”, but when it comes to “opinion testimony” from an attorney who would be testifying for their own client, their testimony is still essentially “disputed fact” for the jury.²⁵

III. Non-Confidentiality of Files of an Expert Witness

The private work notes of an attorney in a trial is information that the other side has no right to access.²⁶ Other private work products of an attorney is information that the other side has no right to access unless the other side can prove that not obtaining it will do a great injustice.²⁷ Attorneys need the ability to investigate both favorable and unfavorable aspects of their client’s case.²⁸ It’s also important to not allow party opponents to take advantage of the opposing counsel’s hard work.²⁹

Many jurisdictions have adopted a rule that the files of testifying expert witnesses are not confidential and can be obtained by another party.³⁰ At the same time, lawyers owe the strictest duty of confidentiality to their clients.³¹ The rules of evidence create Attorney-Client privilege that prevents disclosure of confidential communications between client and lawyer to others.³²

What is a “confidential communication between client and lawyer”?

Information transmitted between a client and his or her lawyer in the course of that relationship and in confidence by a means which, so far as the client is aware, discloses the information to no third persons other than those who are present to further the interest of the client in the consultation or those to whom disclosure is reasonably necessary for the transmission of the information or the accomplishment of the purpose for which the lawyer is consulted, and includes a legal opinion formed and the advice given by the lawyer in the course of that relationship.³³

Thus, in order to testify as an expert witness for their client, an attorney would almost certainly have to disclose information that is subject to attorney client privilege. It would create an irreconcilable conflict, preventing a lawyer from doing their fundamental job as the attorney for that defendant.

IV. Conclusion

With very limited and narrow exceptions, a criminal defendant cannot have their own defense attorney testify as an expert witness at trial. It violates the advocate-witness rule and it threatens strict rules of client confidentiality.

Hope that answers the question!

Do you have a question for Off Script? Send to maxkanin@substack.com!

1. The author of this article is an attorney licensed to practice in the State of California and the District of Columbia. This article and all of the works on this Substack page are statements of the opinions of the author, only, and do not constitute legal advice; they are not intended to be relied upon by any individual or entity in any transaction or other legal matter, past, pending, or future. A paid subscription to this Substack page supports the author’s scholarship and provides access to research that the author has compiled, but does not establish an attorney-client relationship. The author does not accept unsolicited requests for legal advice or representation, and this Substack page is not intended as legal advertising. The opinions expressed on this Substack page reflect the personal views of the author only. In addition to the usual disclaimer, the author does not guarantee that he will answer any question from a subscriber based solely on subscriber status.