What an Expert Witness Does at Each Stage of a Case
A technical case is a long road, and the expert you retain walks most of it with you. The work starts well before the expert report and does not end at deposition. Here is where an expert witness earns their fee, from the day the complaint is filed to the verdict, and where a weak one gets found out.
The complaint
What is happening: A case has been filed, or a client has brought you one that turns on technology.
What your expert does: A consulting expert reads the patents, the product, or the code and tells you early where the case is strong and where it is not. Under the Federal Rules, a consulting expert's work is generally protected from discovery, so this is the place for candid answers.
Contentions
What is happening: In patent cases, the local rules of many districts require early infringement and invalidity contentions.
What your expert does: Maps claim limitations to the accused product or the prior art, so the contentions you serve are ones the evidence will support later.
Claim construction
What is happening: The court decides what the disputed claim terms mean, often after a Markman hearing.
What your expert does: Teaches the judge the technology in a tutorial, and supports your proposed constructions with a declaration.
Discovery
What is happening: Documents, products, and source code are produced, the code usually under a protective order in a locked review room.
What your expert does: Reviews the code, tests or reverse engineers the products, and ties each finding to specific files and versions. In the Toyota unintended acceleration litigation, Barr Group's team reviewed the engine control source code under one of the strictest protective orders in product liability history.
Expert reports
What is happening: Each side discloses its testifying experts and serves their written reports, then rebuttal reports. Under the Federal Rules the default is at least 90 days before trial, with rebuttals 30 days later, but most scheduling orders set their own dates.
What your expert does: Writes opinions that are their own, explains the basis for each one, and drafts with cross-examination in mind from the first page.
Expert deposition
What is happening: Opposing counsel questions your expert under oath about the report and everything behind it.
What your expert does: Answers from work they personally did and directed. This is where the paper expert usually shows: the one who cannot say which files they reviewed.
Daubert
What is happening: The other side moves to exclude your expert under Federal Rule of Evidence 702. Since the December 2023 amendment, the rule says plainly that you must show the court it is more likely than not that the testimony is reliable.
What your expert does: Stands on a method that is documented, repeatable, and tied to the facts of the case. A case can be lost here without a jury ever hearing it.
Trial
What is happening: The expert testifies before the judge or jury, then faces cross-examination.
What your expert does: Teaches the technology in plain language and holds the opinions under pressure. In the 2013 Toyota trial in Oklahoma City, the jury concluded that flaws in Toyota's source code caused the accident at issue.
At the PTAB and the ITC
The stops are similar but the road is shorter. In an inter partes review, expert declarations do much of the work that live testimony does in court; in Rovi v. Comcast, Michael Barr provided the patent owner's expert declaration, and the Board held that the petitioner had failed to prove any challenged claim unpatentable. ITC investigations run on a faster schedule than most district court cases, which leaves less time to replace an expert who does not hold up.
Choose the expert for the whole road
The expert you retain at the complaint has to be the one still standing at trial. Tell us about your case, and within 2 to 3 business days you will have a shortlist of experts who fit it, each vetted by an engineer.
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