Judicial Computer Expert vs. Party Expert: Key Differences in the Forensic Field

The modern forensic professional can no longer be limited to being a lab technician. The evolution of technologies and their growing impact on judicial proceedings demand that the computer expert have a hybrid profile: highly technical, yes, but also legal and a good communicator. Mastery of tools like Autopsy, FTK, Cellebrite, or Oxygen Forensics is not enough. It is essential to understand how distributed systems operate, how audit logs are managed in environments like Microsoft 365, Google Workspace, or Amazon Web Services, and how to extract evidence without breaking the chain of custody or violating essential legal principles.

But beyond investigating, preserving, and analyzing, the expert must be able to communicate. And do it well. Explaining to a judge, a lawyer, or a prosecutor — all generally unfamiliar with technical matters — why a log lacks integrity, how unauthorized access is detected in Exchange Online, or what identity spoofing through SMTP header forgery entails, requires teaching skills. The technical truth must be translatable into legal language.

In this context, the figure of the computer expert gains increasing importance in judicial proceedings where electronic evidence is decisive. And here is where a fundamental distinction arises: is being a court-appointed expert the same as being a party-appointed expert? The short answer is no. The long one deserves this article.

The Party-Appointed Computer Expert

The party-appointed computer expert is the professional hired directly by one of the litigating parties: either the plaintiff or the defendant. Their goal is to prepare a technical expert report that supports their client's legal position, serving as a counterbalance, reinforcement, or refutation against other existing evidence in the proceeding.

Contrary to what many believe, their work does not imply a lack of objectivity. Although their report is part of the evidentiary body of one of the parties, the expert is obliged to maintain technical truthfulness above the interest of the party that hires them. If during their analysis they discover information harmful to their client, they are obliged to include it in their report. It will be the party who decides whether to present it as evidence, but the professional integrity of the expert must not yield to strategic convenience.

Legally, their appointment is supported by Article 338 of the Civil Procedure Law (LEC), which allows the parties to freely propose experts. The party-appointed expert must have official qualifications, as established by Article 340.1 of the LEC, although they do not need to be registered on official lists or necessarily be a member of a professional association.

However, their appointment can be challenged through the disqualification procedure if it is proven that they have family ties, economic interest, or affinity with any of the parties. Therefore, technical impartiality is essential, even when structural impartiality is not guaranteed.

Their field of action is broad: they can intervene in investigations of digital fraud, unauthorized access, email analysis, file integrity verification, reconstruction of event chains, etc. It is common for their report to be submitted along with the claim or response, and even during the hearing as documentary evidence, and in many cases it is ratified in oral trial, where they must face questioning by the court and the opposing party's lawyers.

The Computer Forensic Expert

The judicial expert is appointed directly by the court, either ex officio or at the request of one of the parties when the court considers that a neutral technical assessment is required. Their mission is to be an assistant to the judge: they do not act in defense of a thesis, but as an impartial expert who helps interpret technical issues essential for the ruling.

The appointment of these professionals is regulated by Articles 339 and 341 of the LEC, and to access such appointment it is common —though not mandatory in all cases— to appear on the annual lists of experts prepared by professional associations or by legally recognized associations.

They must have, like the party-appointed expert, official certification in the subject matter of the report (computer science, telecommunications, technical engineering...). And, according to Article 343 of the LEC, before issuing their report they must take an oath or promise of objectivity before the court.

Their functions are similar technically, but different in purpose: they are expected to provide an unbiased analysis aimed exclusively at clarifying disputed facts. The ratification of the judicial report may also be required in trial, and its testimony usually carries significant weight in judicial assessment due to its neutral character.

Legal and Regulatory Framework

The work of both experts is mainly framed within the Law 1/2000, of January 7, on Civil Procedure, which regulates the expert report as a means of evidence (art. 335 et seq.). The most relevant articles are:

• Art. 335 LEC: Defines expert evidence.
• Art. 338 LEC: Allows the parties to freely propose their experts.
• Art. 339 LEC: Regulates the judicial appointment procedure.
• Art. 340 LEC: Requires official certification.
• Art. 341 LEC: Details the lists of experts.
• Art. 343 LEC: Establishes the obligation of objectivity for the judicial expert.

In addition to procedural legislation, expert practice in the technological field must also respect technical standards such as UNE 197001, ISO/IEC 27037, 27042, and 27043 standards, as well as guidelines from organizations like ENISA, NIST, or CCN-CERT, regarding evidence management, traceability, documentation, and principles of good forensic practice.

Conclusion

The figure of the computer expert, whether judicial or party-appointed, is a key pillar in clarifying facts when they have a technological component. Their role goes beyond the technical field and fully enters the administration of justice, where their work can be decisive.

Both roles share the need for solid training, constant updating, and professional ethics. The choice of expert —whether by the court or the parties— can be decisive in the interpretation of the probative fact, and ultimately, in the resolution of the legal conflict.

In an environment where digital crime is increasingly sophisticated and cross-cutting, the professionalization of computer experts is more than a recommendation: it is a necessity.