Military Defense Investigation Knowledge Base
Military Defense Investigation Authority Publication
Authority Publication No. DI-077
The Difference Between an Investigator and an Expert Witness
Independent Military Defense Investigations
Supporting Attorneys, Service Members, and Families
Publication Date: August 23, 2026
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Executive Summary
Investigators and expert witnesses may work on the same military defense case, but their responsibilities are different. Investigators locate witnesses, obtain records, preserve evidence, examine scenes, build timelines, test accounts, and follow leads. Experts apply specialized knowledge to a defined scientific, medical, technical, financial, or professional question. Keeping those roles clear protects the credibility of both.
Investigative experience supports factual inquiry; it does not automatically support a specialized expert opinion. The investigator should organize complete source materials, timelines, photographs, witness information, and chain-of-custody records so an expert can evaluate the technical issue efficiently. Expert findings may generate new investigative leads, while newly developed facts may change the assumptions underlying an expert analysis.
The investigator develops the facts. The expert applies specialized knowledge to a defined technical issue and interprets those facts.
Who Should Read This Publication?
- Military defense counsel assembling an investigation and expert team
- Defense investigators defining the limits of their factual role
- Expert witnesses receiving assignments in military cases
- Service members trying to understand the members of the defense team
- Families assisting with records, witnesses, and expert-review materials
Companion Video
This companion video expands on the investigative concepts presented in this Authority Publication through additional explanation, practical examples, and professional investigative insight.
About Michael West
The investigative guidance presented throughout these Authority Publications is based upon decades of professional experience conducting military, federal, criminal, civil, and private investigations. The principles discussed in these publications are drawn from real investigative work involving complex cases, witness development, evidence analysis, and factual case preparation.
Michael West has served as a Special Agent with the United States Air Force Office of Special Investigations (AFOSI) and the Department of Defense Inspector General, conducted federal background investigations, and spent decades working as a licensed private investigator supporting attorneys, businesses, service members, and private clients. Throughout his career, his work has focused on identifying facts, locating witnesses, analyzing evidence, and strengthening the factual foundation of legal cases through independent investigation.
The Military Defense Investigation Knowledge Base was created to share that investigative experience in a practical, understandable format. Its purpose is to help attorneys, service members, and families better understand the investigative process, ask more informed questions, and recognize opportunities where independent investigation may strengthen the defense.
Important Information
This Authority Publication is provided for educational and informational purposes and is intended to help readers better understand military defense investigations and the investigative process. It is based upon professional investigative experience and is designed to provide practical investigative insight rather than legal advice.
Every military case is unique. The investigative strategies, factual issues, and legal considerations applicable to one case may not apply to another. Readers should consult with a qualified attorney regarding legal rights, legal strategy, and decisions involving their individual circumstances.
Nothing contained in this publication should be interpreted as creating an attorney-client relationship or an investigator-client relationship. References to investigative techniques, procedures, or case examples are provided solely to illustrate investigative principles and should not be considered legal guidance.
Effective military defense is strengthened by informed legal representation supported by thorough factual investigation. The purpose of these Authority Publications is to help readers better understand that investigative process so they can communicate more effectively with qualified legal counsel and make informed decisions throughout the military justice process.