What type of evidence is a private investigator's report? Anatomy of a tertium genus
In the first entry of this series, we explained why the investigator's report has full standing before our courts. But there remains an even more interesting question: what exactly is investigator's evidence? A document? Witness testimony? Expert evidence?
The question is not academic. It determines when the evidence is submitted, how it is examined, how the investigator is questioned, and how the court weighs it.
Before the LEC of 2000: documented testimony
Supreme Court case law had been grappling with this question for years before the LEC of 2000 expressly regulated investigators' reports.
The STS of 19 July 1989 denied the report documentary character for certain procedural purposes. The STS of 6 November 1990 reiterated its connection with witness evidence and, in support of the investigator's credibility, highlighted the professionalism required of a regulated profession, the precise focus on the object of observation, and the supporting photographic or audio material.
The STS of 24 February 1992 used a particularly vivid expression: "improper witness evidence."
The paper documented. The investigator testified. The judge weighed both elements together.
The LEC of 2000 expressly recognises the report
Law 1/2000 took a decisive step. Article 265.1.5 includes reports prepared by legally licensed private investigation professionals on relevant facts on which the parties base their claims.
And the legislator added a specific rule: when the facts recorded in those reports are not acknowledged as true, witness evidence shall be taken.
Article 380 completes the system: the author appears as a witness, proves their licence, acknowledges the report, ratifies its content, and answers questions about the facts it records.
The architecture is distinctive: it is documented in writing, but designed to be defensible orally by the professional who obtained the facts.
A document with someone behind it
An ordinary document is simply there. An invoice is simply there. A photograph is simply there.
Behind the investigator's report stands a legally licensed professional who can appear in court and explain where they were, what they observed, at what time, for how long, from what position, what images they obtained, and what happened before and after.
The opposing party can ask questions. The judge can ask questions. And the investigator answers personally for what they recorded.
Few pieces of private evidence combine document, direct perception, and adversarial examination so naturally.
So, is it documentary or testimonial evidence?
The most prudent answer is that it depends on which aspect we examine and on the jurisdiction.
In civil proceedings, the LEC gives the report a specific written regime for submission and, when its facts are disputed, provides for the witness examination of its author.
In labour proceedings, case law has insisted on its fundamentally testimonial nature for certain purposes, especially when the report is meant to be used as a document capable of revising the facts found proven on appeal.
That is the origin of expressions such as "improper witness evidence," "documented testimony," or "qualified witness."
And is it expert evidence?
As a general rule, no.
An expert witness takes part because they possess the scientific, artistic, technical, or practical knowledge needed to assess facts. The investigator contributes, fundamentally, facts directly perceived.
They don't need medical knowledge to state that a person carried boxes. They don't need to be an economist to prove that someone enters an office every day and deals with clients.
That said, Article 380 allows the report to incorporate assessments grounded in the author's specialised knowledge. When that happens, the law refers to the expert-witness regime.
The tertium genus
In 1999, Professor Fermín Morales Prats and the author of this article published "La naturaleza jurídico-procesal del detective privado. El testigo-perito."
Our reflection started from an obvious singularity: the investigator does not fit the paradigm of the chance witness. Their observation is professional and deliberate. There is an assignment, a purpose, planning, a methodology, and documentation contemporaneous with the facts.
Nor, in their ordinary function, do they fit the expert-witness model, because their principal contribution does not consist of issuing technical opinions but of obtaining and documenting facts.
Hence our proposal to speak of a *tertium genus*. Not because the LEC formally created a fourth general category of evidence called "investigator evidence," but because it established a combination of elements that better explains its nature when viewed as a distinctive evidentiary figure.
Document. Testimony. Professionalism. Direct perception. Photographic or video support. Adversarial examination.
Not just anyone can produce this report
Article 265.1.5 LEC does not speak of reports by private individuals. It speaks of reports prepared by "legally licensed private investigation professionals."
Professional status is itself part of the legal definition of the evidence.
Law 5/2014 completes that status: the investigator must be licensed, act on behalf of a legitimately entitled third party, document the assignment, identify the actions taken, and remain available to ratify their reports when required.
Appearing in court is not some incidental afterthought of the trade. It is part of the investigator's professional status.
Civil, labour and criminal proceedings
In civil and commercial proceedings we find the most clearly defined regime: written submission under the LEC and witness examination when the facts are disputed. Article 380 adds a fundamental rule: questioning is limited to the facts recorded in the report.
In labour proceedings, Article 92 LRJS establishes that witnesses cannot be formally challenged for bias, without prejudice to the parties making observations about their credibility. The investigator's real strength lies in the witness examination conducted at first instance, backed by the report and its supporting material.
In criminal proceedings, the LECrim contains no equivalent specific regulation. If the investigator provides direct knowledge of relevant facts, their testimony as a witness allows them to be cross-examined. And a distinction must always be drawn between the procedural nature of evidence already obtained and the substantive limits of the professional activity: when the assignment specifically consists of investigating an offence, Article 48.1.c) of Law 5/2014 confines that activity to offences prosecutable only at the request of a party and on the instructions of those legitimately entitled to bring it.
Five strategic rules
1. The report is written with its future ratification in mind.
2. Whoever saw it testifies about what they saw.
3. The report sets the boundaries of the future testimony.
4. Fact and inference must be kept separate.
5. When an expert is needed, an expert is brought in.
Investigator and expert witness perform different, complementary functions: one obtains and establishes facts; the other contributes, when necessary, specialised knowledge to interpret them.
Conclusion: a document that breathes
The investigator's report is a document with memory. It has photographs, dates, times, locations, and facts, but behind it stands a professional who perceived them directly and who can sit before a judge to explain exactly how they occurred.
That is why it is insufficient to define it solely as documentary evidence. And it is incomplete to see it exclusively as conventional witness evidence. Nor is it, in its ordinary function, expert evidence.
It is evidence of a distinctive configuration, expressly recognised by our legal system, which combines professional documentation and personal testimony.
A report that doesn't just show what happened. It has someone capable of answering for it.
Truth has a method.