Reference · 60 terms

Forensic and expert-witness glossary

Plain-English definitions covering forensic methods, evidence handling, and the legal standards that govern expert testimony. Written for attorneys and claims teams who need the vocabulary before a first call.

Discipline Method 29

Accident reconstruction

Also: collision reconstruction, crash reconstruction, momentum-energy analysis

Reconstruction of how a collision or incident occurred using physics, including conservation of momentum and energy methods, along with scene measurements, vehicle data, and damage analysis. Results depend on the quality of input data and stated assumptions, which should be documented and tested.

Related: delta-V, cell site analysis

See: accident reconstruction, product liability, human factors

ACE-V

Also: Analysis Comparison Evaluation Verification

A structured framework used mainly in fingerprint and other pattern comparison work, standing for Analysis, Comparison, Evaluation, and Verification. Critics note it documents the steps an examiner follows but does not by itself make the underlying judgment objective or quantify error, so conclusions still depend on examiner interpretation.

See: fingerprint analysis, forensic ballistics firearms

Bias

Also: cognitive bias, contextual bias

Influences that can push an analysis or opinion away from an objective result, including financial interest and exposure to task-irrelevant contextual information. Some laboratories use context management and blind verification to reduce it. Bias is a frequent subject of cross-examination and of quality procedures alike.

See: fingerprint analysis, forensic psychology, bloodstain pattern analysis, forensic document examination

Bite mark analysis

Also: forensic odontology bite mark comparison, bitemark identification

Comparison of injury patterns to a suspect's dentition to assess whether a person could have caused a bite. This discipline has drawn heavy scientific criticism, with independent reviews questioning whether human skin reliably records dentition and whether examiners can accurately match marks to a specific individual.

See: forensic odontology

Bloodstain pattern analysis

Also: BPA, blood spatter analysis

Interpretation of the size, shape, and distribution of bloodstains to infer how blood was shed at a scene. It can support or contradict a proposed sequence of events, but major scientific reviews have flagged that many conclusions rest heavily on examiner experience and can carry substantial uncertainty.

See: bloodstain pattern analysis, forensic pathology

Cell site analysis

Also: historical cell site analysis, CSLI analysis, cell tower analysis

Interpretation of phone records and cell tower connection data to estimate where a device may have been over time. It can suggest general location and movement, but a tower connection does not pinpoint an exact spot, and factors like network load and terrain limit precision, which has drawn scrutiny.

See: digital forensics

Chromatography

Also: gas chromatography, GC, liquid chromatography, GC-MS

A separation technique that splits a mixture into its individual components so each can be measured, commonly paired with a detector such as a mass spectrometer. Gas and liquid chromatography are standard in drug, toxicology, and trace analysis for identifying and quantifying substances.

See: forensic toxicology, trace evidence

Comparison microscopy

Also: comparison microscope analysis, side-by-side microscopy

Use of a microscope that lets an examiner view two items side by side in a single field, common in firearm, toolmark, hair, and fiber work. It supports visual comparison of features, and for pattern disciplines the resulting conclusion still rests on examiner interpretation.

See: forensic ballistics firearms, trace evidence

Delta-V

Also: change in velocity, impact severity

The change in a vehicle's velocity during a collision, a core measure used to estimate crash severity and forces on occupants. It is often derived from vehicle crush data or event data recorders, and its reliability depends on the accuracy of those inputs.

Related: accident reconstruction

See: accident reconstruction, product liability

ESDA

Also: electrostatic detection apparatus, indented writing detection

The electrostatic detection apparatus is an instrument that reveals indented writing, the pressure impressions left on a page beneath the one that was written on. It is a nondestructive technique used in questioned document work to recover text that is otherwise invisible.

See: forensic document examination

Gunshot residue

Also: GSR, firearm discharge residue

Particles produced when a firearm discharges, typically analyzed for characteristic metal components using scanning electron microscopy with elemental analysis. Presence can indicate proximity to a discharge, but residue can transfer between people and surfaces and can be lost over time, so findings require careful context.

See: forensic ballistics firearms, trace evidence

Latent print

Also: latent fingerprint, friction ridge print

A fingerprint left unintentionally on a surface, usually invisible until developed with powders, chemicals, or light. Examiners compare ridge detail to known prints, most often using the ACE-V framework; conclusions are interpretive and can be affected by print quality and examiner judgment.

See: fingerprint analysis

Locard's exchange principle

Also: principle of exchange, every contact leaves a trace

The foundational forensic idea that when two objects or people come into contact, material transfers between them in both directions. It is the theoretical basis for collecting and comparing trace evidence, though it describes a tendency, not a guarantee that recoverable material is always left behind.

Related: touch DNA, gunshot residue

See: trace evidence, forensic dna biology

Luminol test

Also: luminol, chemiluminescent blood test

A presumptive chemical test that glows when it reacts with blood, used to reveal traces that have been cleaned or are not visible. Because other substances can also cause a reaction, a positive result is a lead that requires confirmatory testing, not proof that blood is present.

See: bloodstain pattern analysis, forensic dna biology

Microscopic hair comparison

Also: hair microscopy, microscopic hair analysis

Visual comparison of hair features under a microscope to assess whether samples are similar. It can help include or exclude a source class but cannot by itself identify a specific person, and past overstatement of its power has led to significant scientific criticism; DNA testing of hair is more discriminating.

See: trace evidence, forensic dna biology

Postmortem interval

Also: PMI, time since death

The estimated time elapsed since death, approached through body cooling, rigor, lividity, decomposition, and sometimes insect activity. Estimates are ranges rather than exact times and become less precise as more time passes and as environmental conditions vary.

See: forensic pathology, forensic anthropology

Presumptive and confirmatory testing

Also: presumptive test, confirmatory test, screening and confirmation

A two-stage testing logic where a fast, sensitive presumptive test screens for a possible substance and a more specific confirmatory test verifies its identity. Presumptive tests can give false positives, so a positive screen alone is not treated as a definitive identification.

See: forensic toxicology, trace evidence

Probabilistic genotyping

Also: probabilistic genotyping software, likelihood ratio DNA interpretation

Software-based methods that use statistical models to interpret complex or mixed DNA samples and express results as a likelihood ratio. Adoption is widespread but the approach remains debated, because different software can produce different numbers on the same mixture and validation limits vary by program and sample complexity.

Related: STR analysis, touch DNA

See: forensic dna biology

Proficiency Testing

Also: proficiency test, competency testing

A structured test in which an analyst or laboratory examines samples with known or independently established answers to assess ongoing competence. Results support quality claims and can inform discussion of error and reliability. Accreditation programs commonly require regular participation in proficiency testing.

See: forensic dna biology, forensic toxicology, fingerprint analysis, trace evidence

Questioned document examination

Also: QDE, forensic document examination, document analysis

Analysis of documents whose authorship, authenticity, or alteration is disputed, covering handwriting, signatures, ink, paper, printing, and indented impressions. Examiners compare questioned items to known standards; some sub-areas such as handwriting comparison are more subjective than instrument-based tests.

Related: ESDA, spectrometry, latent print

See: forensic document examination

Skeletal analysis

Also: forensic osteology, skeletal examination

Examination of bones to estimate biological characteristics such as sex, age, ancestry, and stature, and to assess trauma. It is used when remains are decomposed or skeletonized; estimates are expressed as ranges and probabilities rather than exact values.

See: forensic anthropology, forensic pathology

Spectrometry

Also: mass spectrometry, spectroscopy, MS

A family of analytical techniques that measure how a substance interacts with energy, such as mass spectrometry, to identify chemical components. It is widely used to confirm the identity of drugs, residues, and unknown materials and is generally considered an objective, instrument-based method.

See: forensic toxicology, trace evidence

Standard Operating Procedure

Also: SOP, written protocol

A documented, approved method that describes how a specific analysis or process is to be performed in a laboratory or field setting. Following an SOP supports consistency and makes work reviewable by others. Deviations from an SOP are often examined during discovery and cross-examination.

See: forensic dna biology, forensic toxicology, digital forensics, fire origin cause

STR analysis

Also: short tandem repeat analysis, DNA profiling, DNA typing

Short tandem repeat analysis is the standard DNA typing method, measuring the number of repeated sequence units at defined locations in the genome to build a profile. It is well validated for single-source and simple samples; interpretation becomes harder with mixtures, degraded material, or very small amounts.

See: forensic dna biology

Technical Review

Also: peer verification, second review

An independent review of an examiner's work, data, and conclusions by another qualified analyst before a report is finalized. It is a quality-control step intended to catch errors and confirm that conclusions are supported. Some disciplines also use blind or independent verification to reduce the influence of expectation.

See: fingerprint analysis, forensic dna biology, forensic document examination, bloodstain pattern analysis

Toolmark analysis

Also: toolmark identification, striation comparison

Comparison of marks left by tools or firearm parts to determine whether a specific tool or gun could have made them. It relies largely on an examiner's visual judgment of matching striations or impressions, and independent scientific reviews have questioned how well its accuracy and error rates are established.

See: forensic ballistics firearms, trace evidence

Touch DNA

Also: trace DNA, low template DNA, contact DNA

DNA recovered from very small amounts of biological material left when a person contacts a surface, such as shed skin cells. Because the quantity is small, results are more prone to mixtures, transfer from someone who never touched the item, and interpretation difficulty, so context of collection matters.

See: forensic dna biology, trace evidence

Toxicology screening

Also: tox screen, drug testing, blood alcohol analysis

Detection and measurement of drugs, alcohol, and poisons in biological samples, typically an immunoassay screen followed by an instrument-based confirmation such as chromatography with mass spectrometry. Interpretation must account for how substances distribute and change in the body after death or over time.

See: forensic toxicology, forensic pathology

Validation Study

Also: method validation

A study performed to show that a method produces reliable and reproducible results for its intended use before it is applied to casework. It can characterize limitations, sensitivity, and error under defined conditions. Validation records are frequently requested to support the reliability of an analytical method.

See: forensic dna biology, forensic toxicology, digital forensics, forensic audio

Evidence & Chain of Custody 8

Chain of Custody

Also: custody log, evidence trail

The documented, unbroken record of who handled a piece of evidence, when, and for what purpose, from collection through analysis to presentation in court. A complete chain supports the claim that evidence was not altered, substituted, or contaminated. Gaps in the record can be used to challenge the reliability of any analysis performed on that item.

See: digital forensics, forensic dna biology, forensic toxicology, fingerprint analysis

Contamination

Also: cross-contamination, sample contamination

The unintended introduction of outside material or data into a sample or scene, which can distort or invalidate an analysis. Laboratories use controls, clean handling procedures, and blanks to detect and limit it. Allegations of contamination are a frequent line of cross-examination in trace, biological, and chemical evidence cases.

See: forensic dna biology, trace evidence, forensic toxicology, bloodstain pattern analysis

Evidence Integrity

Also: sample integrity, tamper-evident controls

The condition of evidence being intact and unaltered from the time of collection, often supported by sealed and labeled packaging, restricted access, and documented storage conditions. Integrity controls make it harder to argue that an item was contaminated or swapped. It underpins the weight a fact-finder may give to test results.

See: forensic dna biology, forensic toxicology, trace evidence, forensic ballistics firearms

Evidence Preservation

Also: preservation of evidence, litigation hold

The steps taken to keep evidence in its original condition once litigation is reasonably anticipated, including securing physical items and issuing holds to stop routine deletion of records. Proper preservation reduces the risk of spoliation claims. It is often the first practical concern when a forensic examiner is retained.

See: digital forensics, construction defect, product liability, fire origin cause

Forensic image (bit-for-bit)

Also: bit-for-bit copy, disk image, forensic duplicate

An exact copy of a storage device that captures every bit, including deleted and unallocated areas, rather than just visible files. Analysis is performed on the copy so the original is preserved, and the copy's fidelity is confirmed with hash verification.

See: digital forensics

Hash verification

Also: hashing, checksum verification, digital fingerprint

Use of a mathematical function to generate a fixed value that acts as a digital fingerprint of data. Matching hash values before and after copying shows the data was not altered, which supports the integrity of digital evidence.

See: digital forensics

Spoliation

Also: evidence destruction, loss of evidence

The loss, destruction, alteration, or failure to preserve evidence that is relevant to litigation. Depending on the jurisdiction and the party's conduct, a court may impose sanctions or instruct the jury that it may draw an unfavorable inference. It commonly arises with physical samples, digital data, and scene conditions that change over time.

See: digital forensics, fire origin cause, accident reconstruction, construction defect

Write-blocker

Also: forensic write blocker, hardware write blocker

A hardware or software tool that allows a digital investigator to read a storage device without altering its contents. It is used when creating a forensic copy so the original evidence stays unchanged, supporting integrity and chain of custody.

See: digital forensics

Legal Process 9

Cross-Examination

Also: cross, adverse examination

Questioning of a witness by the opposing party, used to test credibility, expose limits in methods or assumptions, and probe bias or the basis for opinions. Leading questions are generally permitted. For experts, cross-examination often targets error rates, alternative explanations, and gaps between data and conclusions.

See: forensic toxicology, bloodstain pattern analysis, accident reconstruction, forensic document examination

Deposition

Also: depo, sworn pretrial testimony

Sworn, out-of-court testimony taken before trial, usually in response to questioning by opposing counsel and recorded by a court reporter. For experts, it is used to explore opinions, methods, and potential weaknesses before trial. Deposition testimony can later be used to impeach inconsistent trial testimony.

See: medical malpractice, forensic accounting, accident reconstruction, forensic psychology

Direct Examination

Also: direct, examination in chief

The initial questioning of a witness by the party who called them, used to present that party's evidence and, for an expert, to explain qualifications, methods, and opinions. Leading questions are generally restricted on direct. It sets up the substance that the opposing side will test on cross-examination.

See: forensic pathology, forensic ballistics firearms, medical malpractice, human factors

Expert Report

Also: Rule 26 report, written report

A written statement, typically required from a retained expert, setting out all opinions to be offered, the basis and reasons for them, the facts or data considered, exhibits used, qualifications, and compensation. It frames and often limits what the expert may testify to at trial. Its completeness is a common subject of pretrial motions.

See: forensic accounting, accident reconstruction, construction defect, forensic document examination

Impeachment

Also: witness impeachment

The process of challenging a witness's credibility, for example by showing prior inconsistent statements, bias, or a lack of qualifications. For experts, prior deposition or published statements are common impeachment material. It affects the weight a fact-finder gives testimony rather than its admissibility.

See: forensic psychology, forensic accounting, medical malpractice

Motion in Limine

Also: in limine motion, pretrial exclusion motion

A pretrial request asking the court to rule on the admissibility of specific evidence or testimony before it is presented to the jury. Parties often use it to seek exclusion of an opposing expert's opinions under standards such as Daubert or Frye. Rulings shape what each side can argue at trial.

See: medical malpractice, product liability, accident reconstruction, forensic toxicology

Rebuttal Expert

Also: rebuttal witness, responding expert

An expert retained to respond to or critique the opinions offered by an opposing party's expert, rather than to present an affirmative case in chief. The scope of rebuttal testimony is usually limited to the subjects raised by the other side. Disclosure deadlines for rebuttal experts often differ from those for primary experts.

See: forensic accounting, accident reconstruction, construction defect, human factors

Rule 26 Disclosure

Also: expert disclosure, Rule 26(a)(2)

The federal requirement that parties disclose expert witnesses and, for retained experts, provide a written report and related information within court-set deadlines. It governs what an expert must reveal about opinions, bases, qualifications, compensation, and prior testimony. State courts have their own disclosure rules that may differ.

See: forensic accounting, product liability, construction defect, medical malpractice

Voir Dire of an Expert

Also: expert voir dire, qualification examination

A focused questioning of a proposed expert, often outside the main testimony, to test qualifications, methods, and the basis for opinions before the expert is allowed to testify or be accepted in a field. Opposing counsel may use it to challenge admissibility or limit the scope of testimony. It is separate from voir dire of prospective jurors.

See: forensic psychology, medical malpractice, accident reconstruction, forensic pathology

Standards & Admissibility 14

Accreditation

Also: laboratory accreditation

Formal recognition by a third-party body that a laboratory meets defined quality and competence requirements, often assessed against international standards. In US forensic practice, laboratory accreditation is offered by bodies such as ANAB (the ANSI National Accreditation Board). Accreditation addresses laboratory systems and does not by itself validate any single result.

See: forensic dna biology, forensic toxicology, forensic ballistics firearms, trace evidence

Admissibility

Also: admissible evidence

Whether a court will allow particular evidence or testimony to be considered by the fact-finder under the applicable rules of evidence. It is decided by the judge and is distinct from how persuasive the evidence is once admitted. This directory provides procurement education only and does not assess whether any specific evidence will be admitted.

See: digital forensics, forensic audio, forensic document examination, forensic ballistics firearms

Certification

Also: individual certification, board certification

A credential attesting that an individual practitioner has met a certifying body's requirements in a specific discipline, distinct from laboratory accreditation. Examples of certifying or professional bodies in US forensic practice include the American Board of Forensic Document Examiners and the American Board of Forensic Toxicology. Buyers should confirm any claimed certification directly with the issuing body.

See: forensic document examination, forensic toxicology, forensic odontology, forensic pathology

Daubert Standard

Also: Daubert, Daubert factors

A framework used by federal courts and many state courts for deciding whether expert testimony rests on a reliable foundation, established by the U.S. Supreme Court in Daubert v. Merrell Dow Pharmaceuticals. It asks the judge to act as a gatekeeper and weigh factors such as testability, peer review, known or potential error rate, and general acceptance. This is buyer-education context only and does not predict how any court will rule.

See: forensic toxicology, medical malpractice, accident reconstruction, human factors

Error Rate

Also: known error rate, potential error rate

An estimate of how often a method produces incorrect results, which courts may consider when weighing the reliability of a technique under Daubert. It can come from validation studies or proficiency testing where those exist. Some disciplines have better-characterized error rates than others, which affects how the method is scrutinized.

See: fingerprint analysis, forensic dna biology, forensic ballistics firearms, forensic document examination

Federal Rule of Evidence 702

Also: FRE 702, Rule 702

The federal rule governing testimony by expert witnesses. It permits a qualified expert to offer opinions when the testimony is based on sufficient facts or data, is the product of reliable principles and methods, and those methods are reliably applied to the facts of the case. Many states model their expert rules on it.

Related: Daubert Standard, Rule 703

See: medical malpractice, forensic accounting, product liability, forensic psychology

Foundation

Also: laying a foundation, evidentiary foundation

The preliminary evidence a party must present to show that an item or opinion is what it claims to be and is reliable enough to admit, such as establishing chain of custody or an expert's qualifications and methods. Without adequate foundation, testimony or exhibits may be excluded. It is a threshold matter decided before the substance is weighed.

See: digital forensics, forensic audio, fingerprint analysis, forensic document examination

Frye Standard

Also: Frye, general acceptance test

An older admissibility test, from Frye v. United States, under which scientific evidence is admissible only if the method has gained general acceptance in the relevant scientific community. Some states still apply Frye or a variation of it rather than Daubert. The governing standard depends on the jurisdiction hearing the case.

See: forensic ballistics firearms, bloodstain pattern analysis, forensic document examination, fingerprint analysis

General Acceptance

Also: accepted in the field, peer acceptance

The degree to which a method or theory is recognized as valid by the relevant scientific or technical community. It is the core question under the Frye standard and one of several factors a court may consider under Daubert. It is not the same as proof that a method is correct in a given case.

See: forensic document examination, forensic ballistics firearms, fingerprint analysis, accident reconstruction

Ipse Dixit

Also: because I say so, bare assertion

A Latin phrase meaning an assertion offered on the authority of the speaker alone, without supporting reasoning or data. Courts use it to describe expert opinions that lack a demonstrable connection between the evidence and the conclusion, an idea associated with General Electric Co. v. Joiner. Such opinions are vulnerable to exclusion because the reliability cannot be examined.

Related: Foundation, Daubert Standard

See: forensic accounting, human factors, product liability, medical malpractice

NFPA 921

Also: NFPA 921 guide, fire investigation guide

A widely referenced guide for fire and explosion investigations that promotes a systematic, evidence-based approach to determining origin and cause. It is a consensus guide used to structure investigations; naming it describes methodology and is not a claim about any specific case outcome.

See: fire origin cause, product liability

Peer Review

Also: publication peer review

Evaluation of a method or study by other experts in the field, often through publication in scientific literature. Whether a technique has been peer reviewed and published is one factor courts may weigh under Daubert. It is distinct from the case-level technical review of an individual examination.

See: forensic toxicology, forensic dna biology, human factors, medical malpractice

Qualifications

Also: expert qualifications, credentials

The knowledge, skill, experience, training, or education that supports a person being permitted to testify as an expert in a specific field. Courts assess qualifications when deciding whether to admit expert testimony and how to define its scope. A curriculum vitae, certifications, and prior testimony are common points of inquiry.

See: forensic anthropology, forensic odontology, human factors, construction defect

Rule 703

Also: FRE 703, bases of expert opinion

The federal rule addressing the facts or data an expert may rely on to form an opinion, including material that is not itself admissible if experts in the field reasonably rely on that kind of information. It sets limits on disclosing otherwise inadmissible underlying data to the jury. It works alongside Rule 702 on the substance of expert opinions.

See: forensic accounting, medical malpractice, forensic toxicology, forensic pathology

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