The private investigator's report before the judge: how to build a report that withstands challenge
There's a scene that repeats itself in law firms across Spain: the lawyer has the case won on paper, but is missing the fact. The cohabitation they can't prove, the unfair competition they suspect, the fraudulent sick leave everyone talks about and no one proves.
And then the same question always comes up: "What if we hire a private investigator? Does that hold up in court?"
The short answer is yes. The full answer — the one that can separate effective evidence from evidence that gets challenged or excluded — requires understanding how the report enters the proceedings, what limits the investigation has, and what happens when the investigator sits down in front of a judge.
The procedural basis: Article 265.1.5 LEC
A private investigator's report is not an exotic form of evidence. The Spanish Civil Procedure Act (LEC) expressly recognizes it. Article 265.1.5 covers reports prepared by legally licensed private investigation professionals on relevant facts that the parties rely on to support their claims.
And it adds something decisive: when those facts are not accepted as established, witness evidence will be taken.
Article 380 LEC completes the system. The investigator acknowledges the report, ratifies its content under oath, and answers questions about the facts recorded in it. They don't appear to reconstruct a different investigation or to introduce new facts that were never documented: they appear to explain and stand behind what they observed and professionally recorded.
Even before the 2000 LEC, case law already linked the report's evidentiary weight to its author's testimony. The current regulation sets up a distinctive regime: the report is submitted in writing and, when its facts are disputed, it is completed through the witness testimony of whoever obtained them.
In the labour jurisdiction there is also a particularly important boundary: Article 90.2 LRJS, together with Article 11.1 LOPJ, bars the use of evidence obtained directly or indirectly through procedures that violate fundamental rights.
Lawfulness is not a secondary issue. It is part of the evidence itself.
A singular type of evidence: written report and witness ratification
For decades there has been debate over exactly what the private investigator's procedural nature is. In 1999, Professor Fermín Morales Prats and the author of this article addressed this question in "The legal-procedural nature of the private investigator. The witness-expert."
The investigator doesn't fit the model of an accidental witness: they observe precisely because they have received a professional assignment. But nor are they, as a general rule, an expert witness: their essential function is to describe facts they have directly perceived and, on many occasions, documented through photographs, video, or other media.
The LEC resolves much of this debate procedurally: the report's author testifies as a witness and, when they incorporate assessments based on specialized knowledge, the witness-expert regime may come into play.
What truly matters isn't the label. It's who observed the facts.
An investigation's strength increases when the person who appears in court is precisely the professional who carried out the surveillance, witnessed the conduct, and documented the facts. If someone who wasn't directly involved testifies instead, their knowledge will be indirect regarding what they didn't see.
At Método 3 we hold to a simple rule: whenever possible, whoever carried out the operation is the one who defends in court what they saw.
Three requirements that shape an investigation
First: licensing
The investigation must be carried out by legally licensed private investigators. Law 5/2014 on Private Security establishes the professional framework for the activity and sets out functions, scope, obligations, and responsibilities.
Licensing isn't a mere formality: it identifies the professional as meeting the legal requirements to practise. That said, action taken by an unlicensed person may create liability without it automatically following that all information obtained is constitutionally unlawful. Procedural exclusion also requires analysing how the evidence was obtained and which rights were affected.
Second: lawfulness and proportionality
The investigator may look into conduct that takes place in public spaces or spaces open to legitimate access, within legal limits. They may not enter private homes or investigate private life carried out within them or in other reserved places.
The Private Security Act also imposes four principles that should be present in every operational decision: reasonableness, necessity, suitability, and proportionality.
Is it necessary to observe from that vantage point? Is it proportionate to record that conduct? Is there a less invasive way to establish the same fact? Does what's being documented relate to the legitimate purpose of the assignment?
Article 18 of the Spanish Constitution is not the investigator's enemy. It is one of their main limits — and, precisely for that reason, an essential part of their methodology.
Third: legitimate interest
Investigations aren't carried out out of curiosity. The client must hold a right or legitimate interest regarding the facts under investigation, and must establish this before the assignment is accepted.
This means the future strength of an investigation begins long before the first surveillance operation. It begins when the investigator asks the client why they want to investigate, what their relationship to the facts is, and what legitimate purpose they're pursuing.
When badly obtained evidence backfires
If obtaining evidence involves violating a fundamental right, the consequence may be its exclusion from the proceedings, and in certain circumstances that unlawfulness can extend to other evidence derived from it.
But we should be precise here: in our system there is no automatic, unlimited contamination of everything that follows unlawfully obtained evidence. Constitutional case law examines what's known as the "connection of unlawfulness" between the original violation and the subsequent evidence.
That's why a poor operational decision can be decisive. An unnecessarily invasive recording can turn compelling evidence into a constitutional argument about privacy.
In the "Legal Handbook on Private Investigator Services and Their Reports" I stress an idea that sums up decades in the courtroom: the investigator doesn't work for the client's present, but for the trial's future.
Every operational decision — where to position yourself, from where to observe, what to record, what not to record, and how to preserve the recording — is also an anticipated procedural decision.
The Método 3 standard
Our protocol starts from one premise: every report must be written assuming the opposing party will try to challenge it.
Full traceability: date, time, place, professional involved, sequence, and recording media.
Separating fact from inference: "enters at 10:14 and leaves at 12:26" is a fact; "works there" may be a conclusion that needs more evidence.
Preparing for ratification: reviewing the file, knowing the proceedings, and being ready to explain precisely how the investigation was carried out.
Integrity and authenticity: preserving originals and using systems that can establish the integrity of the recordings and of the report itself.
Conclusion: the evidence that holds up
A private investigator's report can be an extraordinarily effective piece of evidence. It combines facts directly perceived by a professional, contemporaneous documentation, and the possibility that whoever observed them will answer for them before the court.
Its strength doesn't come from any special presumption of truthfulness. An investigator is not a notary. Its real value lies in the lawfulness of the investigation, the precision of the observation, the traceability of what was done, the integrity of the recordings, and the investigator's ability to explain exactly what happened.
The difference between an investigation that holds up and one that falls apart is rarely down to luck.
It's down to method.
Truth has a method.