By Michael Barr
Note: This article offers practical guidance for attorneys engaging technical experts. It is general commentary, not legal advice. The treatment of expert materials in discovery varies by jurisdiction and by the facts. Consult your own counsel about any specific matter.
As a consultant, I think with the trial team. I can tell them a theory is weak, that a document cuts against us more than counsel realizes, or that the honest reading of the code doesn't support what someone hoped it would. As a testifying expert, everything I look at (and much of what I write) is something opposing counsel may hold up at deposition. Both roles are useful. Confusing them is expensive.
The two roles
A consulting expert is retained to help the legal team understand the technology and evaluate the case. They do not testify. They can be candid in ways a testifying expert cannot, because their role is to inform the team's judgment rather than to persuade a fact-finder.
A testifying expert forms opinions that will be disclosed, produces a report, sits for deposition, and may take the stand. Their independence is the source of their value, and it is the first thing opposing counsel will attack.
The distinction exists mainly because the discovery rules treat the two differently. Broadly, and subject to the jurisdiction and the particular rules in play, the materials and opinions of a testifying expert are substantially discoverable, while facts known and opinions held by a non-testifying consulting expert are protected except in exceptional circumstances. Counsel should make the actual determination for the case at hand; the practical point for the technical side is that the protection is real, it is not absolute, and it is easy to forfeit inadvertently.
What a consulting expert is genuinely for
Some of the highest-value technical work in a case is work that will never be filed.
Early case assessment. Before a complaint is drafted or a defense is chosen, someone needs to say whether the technical theory holds up. That conversation is far more useful when the engineer can be blunt, and when a wrong first impression will not later be quoted back to them.
Testing the theory that lost. Good technical evaluation involves considering explanations and discarding them. A consulting expert can explore five theories and abandon four without those four becoming exhibits.
Reading the other side's expert. Understanding where an opposing report is weak, what to ask at deposition, and which of its assumptions will not survive scrutiny is analytical work that supports cross-examination without itself becoming evidence.
Scoping the expensive work. Whether a source code review needs three weeks or three months, whether physical testing is necessary, and what a realistic budget looks like are questions best answered by an engineer who has seen the production, before anyone commits.
Helping counsel learn the field. In a technology case counsel has to become conversant quickly. A consulting expert can teach without the teaching becoming a disclosure question.
The cost difference, and when it matters
The two roles are also priced differently, and in the searches we run that is often the reason the question comes up in the first place.
A testifying expert's rate reflects more than technical skill. It reflects a record of reports, depositions and trial testimony, which an attorney pays for because a fact-finder will be watching. A consulting role does not call for that record. Counsel needs someone who knows the technology and will say what they see, so an engineer with deep experience and no testimony history is a good fit, and usually a less expensive one.
That matters most before anything is filed. A company weighing its patents against a dozen possible infringers may never sue any of them, and every hour spent evaluating each one comes out of an operating budget. At that stage cost is frequently the first constraint counsel raises with us. Once a complaint is filed, the money more often comes from a litigation budget, sometimes from a litigation funder, and the hourly rate stops being the deciding factor.
Source code review is where the difference compounds. A large production can take hundreds of hours to read, trace and catalog. Staffing those hours with consulting reviewers, and reserving the testifying expert for directing the work and verifying what their opinions rest on, costs far less than having the most expensive person on the team do all of it.
Those savings are real. They are also how the next problem usually starts, because the affordable consultant from month one is still there when someone has to testify.
The conversion problem
The most common mistake I see is retaining one person to consult early and then converting them to the testifying role once the case takes shape. It seems efficient. They already know the technology, the documents and the theory.
The difficulty is what came with that history. Everything the person saw, was told, and wrote while consulting may become fair game once they testify, and the protection that applied to the consulting phase may not survive the change of role. Candid early assessments, including the ones that turned out to be wrong, can end up being explored at deposition.
There is a subtler cost as well. A testifying expert's credibility rests on having reached their opinions independently from the evidence. Someone who spent months inside the trial team's strategic deliberations before forming an opinion is more vulnerable to the suggestion that the opinion was arrived at collaboratively, whatever the truth of it.
None of this makes conversion impossible, and sometimes it is the right call. But it should be a decision made deliberately, with counsel's judgment on the discovery consequences in the relevant jurisdiction, rather than a default that arrives because nobody planned the roles.
When one person can do both, and when they should not
If a matter is small, if the technology is narrow, and if the analysis will be straightforward, one expert may reasonably serve throughout. The cost of separation is real and not every case justifies it.
Separation earns its keep when any of the following is true. The technology spans more than one discipline, so the person who scopes the work is not the person best placed to testify about all of it. The case is likely to involve genuinely exploratory analysis where several theories will be tried and discarded. The technical facts may turn out to be unfavorable, and the team needs a candid assessment before committing. Or the eventual testimony will be central enough that the testifying expert's independence needs to be unimpeachable.
That last consideration deserves emphasis in patent infringement and trade secrets matters where a single expert carries the technical case. The value of an expert who can say, truthfully, that they formed their opinions from the evidence and were not part of the strategic conversation is considerable, and it cannot be recovered once it is spent.
How this plays out in practice
A pattern that works well in technology cases: a consulting expert engaged at the outset to assess the theory, scope the technical work and help counsel get fluent; a separate testifying expert retained once the shape of the case is settled, given the evidence rather than the deliberations, and allowed to reach their own conclusions.
Where a large source code review is involved, this maps onto the review structure naturally. The testifying expert directs and verifies the analysis that supports their opinions, while broader exploratory work, including the paths that lead nowhere, can sit on the consulting side. The essential requirement, that the testifying expert genuinely directed and can defend the review underpinning their report, is set out at length in our guide to vetting a source code review team, and separating the roles does not relax it.
One caution worth stating plainly: separation is not a device for insulating unhelpful findings. A consulting expert's analysis that contradicts the testifying expert's opinion is a problem to be confronted, not a document to be filed away. Experts notice when they are being used that way, and good ones decline the engagement.
Questions worth settling at retention
Which role is this person being retained in, and is it documented. Who will they communicate with, and about what. What happens to their work product if their role changes later. Will the testifying expert receive the consulting expert's materials, and has counsel considered the consequences. And, most practically: if this matter goes to trial in eighteen months, is this the person we want on the stand.
Answering the last one at the beginning is what prevents the conversion problem, because the honest answer is often no, and it is much cheaper to know that in month one.
What we do at Barr Group
Because we place experts rather than fielding a fixed bench, we can staff both roles from our directory of electronics and software expert witnesses without the awkwardness of a firm that needs the same person billed on every matter. We ask which role is being filled before recommending anyone, because the right consulting expert and the right testifying expert are frequently different people: the first needs breadth and candor, the second needs depth in the specific technology and the ability to teach it under pressure. Where a matter needs both, we keep the separation clean and make sure the expert reports and testimony rest on work the testifying expert actually directed.
The takeaway
The two roles solve different problems. Use a consulting expert when you need candor, exploration and an honest read on whether the theory holds. Expect that role to cost less, and use it where budgets are tightest: before filing, and across the long hours of a large code review. Use a testifying expert when you need independent opinions that will withstand cross-examination. Decide which is which at retention rather than drifting into it, because converting one into the other late carries discovery consequences and costs credibility that cannot be bought back. And ask the uncomfortable question early: is this the person we want on the stand in eighteen months. If the answer is no, they are your consulting expert, and that is a perfectly good thing to be.
Barr Group's team of electronics and software expert witnesses provide experienced and unbiased source code reviews, expert reports and testimony for product liability, patent infringement, software copyright, and trade secrets litigation involving computer-based technology and software. HIRE AN EXPERT
Get a matched recommendation >
Free, confidential, conflicts-checked, and our fee is built into the expert's hourly rate, so we are paid only if you retain.