Daubert Challenges to Digital Evidence
- SCOPE
- Federal courts + Daubert states
- RULE STATE
- FRE 702 as amended 12/01/2023
- READ TIME
- 9 min
A Daubert challenge asks the judge to exclude an expert before the jury ever hears them. Under Rule 702 as amended December 1, 2023, the proponent must show it is more likely than not that the opinion rests on sufficient facts or data, reliable principles and methods, and a reliable application of those methods to the facts of the case.
What is the Daubert standard?
The Daubert standard is the federal test that requires a trial judge to act as a gatekeeper and admit expert testimony only if it is both relevant and reliable.
It comes from Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), which held that the Federal Rules of Evidence displaced the older “general acceptance” test and put the reliability question in the judge’s hands rather than the field’s.
Two companion cases complete the trilogy and both get cited in digital-evidence motions. General Electric Co. v. Joiner, 522 U.S. 136 (1997), reviews an exclusion only for abuse of discretion and holds that nothing requires a court to admit opinion evidence “connected to existing data only by the ipse dixitof the expert,” because there can be “too great an analytical gap between the data and the opinion proffered.” Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999), extends gatekeeping past scientific testimony to technical and other specialized knowledge, while giving the trial court broad latitude in deciding how to test reliability.
Kumho Tire is the one that settles the threshold question here. Digital forensics is not a laboratory science with a published error rate for every operation, and examiners occasionally argue that Daubert therefore does not really fit. It fits. The gate is the same gate; only the tools for testing reliability change.
What did the December 2023 amendment to Rule 702 change?
The amendment took effect December 1, 2023, and did two things. Both cut against loose expert practice.
A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the proponent demonstrates to the court that it is more likely than not that: (a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.
First, the burden is now written into the rule. The proponent must demonstrate each of (a) through (d) by a preponderance — “more likely than not.” The advisory committee added that language because many courts had been treating the sufficiency of an expert’s basis and the reliability of the methodology as questions of weight for the jury rather than admissibility for the judge. If you have been told that methodological defects “go to weight,” that answer is weaker after 2023 than it was before.
Second, subdivision (d) now targets application, not just method. The opinion must reflect a reliable application of the principles and methods to the facts of this case. The advisory committee note is unusually direct about why: expert overstatement was one of the principal concerns driving the amendment, forensic experts should avoid assertions of absolute or one-hundred-percent certainty where the methodology is subjective, and experts should not assert a degree of confidence not derived from sufficient facts or data and a reliable methodology.
The practical effect on digital forensics is specific and large. A well-validated tool operated carelessly, or operated correctly and then stretched into a conclusion it cannot carry, is now squarely an admissibility problem rather than cross-examination fodder.
What are the four Daubert factors?
Daubert set out four non-exclusive factors a court may use to test reliability. They are guideposts, not a checklist — Kumho Tire confirmed the trial court decides which of them, if any, are reasonable measures for the discipline in front of it.
| FACTOR | WHAT THE COURT ASKS | WHAT IT LOOKS LIKE IN A DIGITAL FORENSIC EXAMINATION |
|---|---|---|
| 1. Testability | Can the theory or technique be tested, and has it been? | A write-blocked acquisition, a recorded hash, and documented parsing steps can be re-run by the opposing examiner against the same image and should produce the same output. Work that cannot be reproduced cannot be tested. |
| 2. Peer review and publication | Has the method been exposed to outside scrutiny? | Published artifact research, vendor and independent documentation of how a parser interprets a structure, and community guidance such as SWGDE and NIST SP 800-86. |
| 3. Known or potential error rate, and standards controlling the technique's operation | How often is it wrong, and what governs how it is run? | NIST Computer Forensic Tool Testing (CFTT) reports for the tool and function relied on, documented tool limitations, written laboratory procedures, and ISO/IEC 17025 accreditation where the lab holds it. |
| 4. General acceptance | Is the technique accepted in the relevant community? | Whether working examiners actually use this tool and this interpretation — as opposed to a bespoke script written for this matter and never validated against known data. |
How does Daubert differ from Frye, and which applies to my case?
Daubert governs in every federal court and in most states. A minority of states still apply the older Frye “general acceptance” test or a local variant of it, which changes what you have to prove and where the fight happens.
| DAUBERT / FRE 702 | FRYE | |
|---|---|---|
| Source | Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579 (1993); codified and refined in FRE 702, amended Dec. 1, 2023 | Frye v. United States, 293 F. 1013 (D.C. Cir. 1923) |
| Core question | Is the methodology reliable, and was it reliably applied to these facts? | Is the technique generally accepted in the relevant field? |
| Judge's role | Gatekeeper who assesses the methodology and its application directly | Narrower — surveys the field's acceptance rather than auditing the method |
| General acceptance | One non-exclusive factor among several | The entire test |
| Reach | All expert testimony, technical and specialized as well as scientific (Kumho Tire) | Typically reserved for novel scientific evidence; established or non-scientific methods often escape the screen |
| Burden | On the proponent, by a preponderance — more likely than not | Varies by jurisdiction |
| Effect on digital forensics | A mainstream tool is not enough on its own; the examiner's application to this evidence is examined | A mainstream, accepted tool generally clears the bar, and the contest shifts to weight at trial |
| Where it governs | All federal courts and the large majority of states | A minority of states, including California, Illinois, New York, Pennsylvania, and Washington |
How do digital forensic opinions actually get excluded?
Almost never because hashing does not work. Exclusion turns on what the examiner did, whether it was written down at the time, and whether the opinion outran the data. Six failure modes account for most of it.
› 1. Undocumented methodology
The challenge.The report says the examiner “imaged the device and analyzed it,” with no acquisition tool, no version, no hash, no settings, and no sequence of steps. Opposing counsel cannot reproduce anything, and neither can the court. Under 702(c) and (d) there is simply nothing to evaluate, and the burden is on the proponent.
The answer. Contemporaneous examination notes, with the tool and version recorded at each step, and a report written so that a competent examiner handed the same source material can re-run the work and reach the same result.
› 2. Tool validation
The challenge. The examiner cannot say whether the tool was ever tested for the specific function the opinion depends on, or relied on a one-off script written for this matter and never run against known data. Factor three has nothing to attach to.
The answer.Cite the tool’s testing record, including NIST CFTT reports where they cover the function; state the tool’s known limitations before the other side does; and corroborate any load-bearing artifact with a second tool or by parsing the underlying structure by hand.
› 3. Unverified hashes
The challenge.No acquisition hash, no verification hash, or a mismatch nobody addressed. This is an authentication problem as much as a reliability one: FRE 901(b)(9) asks for evidence describing a process or system and showing that it produces an accurate result, and FRE 902(14) — the self-authentication route for data copied from a device — is built entirely on authentication “by a process of digital identification.” Without hashes you have given both away.
The answer. Record acquisition and verification values for every item, and document any mismatch together with its cause at the time it occurs, rather than leaving it for a deposition to discover.
› 4. Gaps in the chain of custody
The challenge. Unexplained transfers, no record of seal or storage, or a device that is unaccounted for between collection and examination. Custody gaps usually go to weight — but a gap wide enough, paired with any other defect on this list, becomes an admissibility argument, and it reliably costs the expert credibility with the bench.
The answer. One custody record per item, opened at collection, showing every custodian, date, transfer, storage location, and access.
› 5. Overstated certainty
The challenge. “Conclusively,” “one hundred percent certain,” or — the common one in this field — attributing an act to a person when the artifact establishes only an account or a device. This is the exact failure the 2023 advisory committee note names, and it is now a 702(d) argument rather than a cross-examination point.
The answer. State each conclusion at the level the artifact actually supports, keep the device and the user distinct, and identify the alternative explanations along with what in the evidence does or does not rule them out.
› 6. Scope creep beyond the expert’s expertise
The challenge. A computer examiner opining on mobile chip-off recovery, on damages, on what a party intended, or on the ultimate legal question. Rule 702 qualifies a witness in a field; it does not qualify them for the whole case.
The answer. Define the boundaries of the assignment in the report, decline questions outside them on the record, and retain a second expert rather than stretching one past their qualifications.
How do I challenge the other side’s digital forensics expert?
Work the record before you work the brief. A Daubert motion built on what the examiner did is far harder to answer than one built on what the examiner concluded.
- Get the underlying material, not just the report. The forensic image or a working copy, hash values, raw tool output and exports, examination notes, and the name and version of every tool. Rule 26(a)(2)(B)(ii) already entitles you to the facts or data the witness considered.
- Compare the report against the notes. Opinions that appear in the report but have no counterpart in the contemporaneous notes are usually the ones that will not survive a deposition.
- Re-run the work. Have your own examiner verify the hashes and independently reproduce the key findings from the same source. A finding that does not reproduce is not an argument about weight — it is the motion.
- Pin the methodology down at deposition. Tool, version, settings, validation, what was examined, what was not examined and why. Then ask what result would have changed the opinion. An expert who cannot answer that has not tested anything.
- Pull the four-year testimony list. Rule 26(a)(2)(B)(v) requires a list of all cases in which the witness testified at trial or by deposition in the previous four years. Read the transcripts and any admissibility rulings. A prior inconsistent description of the same method is worth more than a prior exclusion.
- Separate the reliable core from the overreach. Concede the clean acquisition if it is clean. Aim the motion at the inference — the step where the data stops and the opinion keeps going.
- File on the methodology, not the conclusion. Joiner is the citation for the analytical gap; amended 702(d) is the citation for a sound method applied unsoundly; and the 2023 committee note is the citation for overstated confidence.
How do I make my own expert’s work survive a Daubert motion?
The defensive work is done during the examination, not during the briefing. By the time a motion is filed, the record either supports the opinion or it does not.
- Engage before the evidence moves. Acquisition decisions made in the first week determine what can be defended two years later, and the duty to preserve electronically stored information attaches when litigation is anticipated — well before a complaint is filed. Fed. R. Civ. P. 37(e) governs what happens when that duty is missed.
- Document contemporaneously, not at report time. Notes reconstructed after the fact read exactly like notes reconstructed after the fact.
- Corroborate anything load-bearing. If an opinion rests on one artifact parsed by one tool, verify it a second way before it goes in the report.
- Write the report to Rule 26(a)(2)(B) completely. A complete statement of every opinion with basis and reasons; the facts or data considered; exhibits; qualifications with ten years of publications; the four-year testimony list; and compensation. Incomplete disclosure is a cheaper way to lose an expert than Daubert is.
- Calibrate the language. Every conclusion pitched at the confidence the evidence supports, and every plausible alternative explanation addressed rather than ignored.
- Hold the scope line.The strongest expert on the stand is the one who says “that is outside what I examined” and means it.
Frequently asked questions
Does Daubert apply to digital forensics if it is not a science?
Yes. Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999), held that the trial judge's gatekeeping obligation extends to testimony based on technical and other specialized knowledge, not only scientific knowledge. A digital forensic examiner faces the same reliability screen as a toxicologist, though the factors used to apply it differ.
When is the deadline to file a Daubert motion?
The Federal Rules set no deadline. It comes from the scheduling order under Rule 16(b), and courts commonly set it with dispositive motions or at the final pretrial conference. Read the scheduling order and the judge's standing order early, because untimely challenges are routinely denied and the objection is then left to weight rather than admissibility.
Does a Daubert challenge require an evidentiary hearing?
No. A court may rule on the papers when the record is adequate, and often does. A hearing is more likely where the dispute turns on what the examiner actually did — which tool, which settings, which verification steps — rather than on whether the underlying method is sound in the abstract.
Does a hash mismatch destroy the evidence?
Not by itself. Mismatches have legitimate causes, most obviously a live acquisition from a running system whose state changes while it is being read. What damages an opinion is a mismatch the examiner never recorded, never noticed, or cannot explain, because it leaves the court no way to tell error from alteration.
Is a prior exclusion disqualifying for an expert witness?
No, and it is not unusual among experts with long testimony records. What matters is the reason. Exclusion for exceeding the scope of a designation or for a discovery default says little about competence. Exclusion for unreliable methodology is a genuine problem the next time the same method is offered.
Can I attack only part of an expert's opinion?
Yes, and it is often the stronger motion. Courts trim opinions more readily than they strike experts wholesale. A motion that concedes a clean acquisition and targets the inference drawn from it reads as credible; a motion attacking everything invites the court to treat the whole filing as argument about weight.
Law & Forensics provides digital forensic examinations and expert testimony framed for Rule 702 reliability, and rebuttal analysis of opposing examinations. If digital evidence is in play in your matter — start a scoping conversation or reach us directly below.
Related reading: How to hire and vet a digital forensic expert witness.
// ATTORNEY ADVERTISING / EXPERT SERVICES. GENERAL INFORMATION ABOUT EVIDENCE LAW AND FORENSIC PRACTICE — NOT LEGAL ADVICE, AND NOT A SUBSTITUTE FOR CHECKING THE RULES AND CASE LAW OF YOUR OWN FORUM.