Unchallenged Expert Evidence: Why It Is Deemed Accepted at Trial
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lightbulbKey Takeaways
- check_circleUnchallenged expert evidence is deemed accepted
- check_circleDisagree in the provisional pleadings
- check_circleQuestion the expert at trial (Art. 724 LECrim)
- check_circleIt cannot be challenged first on cassation
Quick answer
The Spanish Supreme Court, in its judgment of 28 May 2026 (appeal 10709/2025), recalls that where the defence does not express in its provisional pleadings (escrito de calificación provisional) its opposition to or disagreement with the expert report, nor ask for its clarification or expansion, that report becomes established evidence, implicitly accepted and consented to. Objections about the expert's methodology or shortcomings must therefore be raised at the proper procedural stage — the trial hearing, in line with Article 724 of the Criminal Procedure Act (LECrim) — and not for the first time on cassation. A party that does not challenge the report in due time and form leaves it consolidated as incriminating evidence and loses the chance to dispute its validity later.
In many criminal proceedings, expert evidence is the axis on which conviction or acquittal turns: a technical report the court could not produce on its own, on which it grounds its conviction about facts that demand specialised knowledge. That is why the manner and the moment of disputing it matter so much. The Spanish Supreme Court, in its judgment of 28 May 2026 (appeal 10709/2025), recalls a rule of procedural discipline with great practical reach: an expert report that the defence does not challenge in its provisional pleadings is deemed accepted, and objections about the expert must be raised at the trial hearing, not for the first time on cassation. We comment below on the scope of this doctrine, for general information and not as advice on any specific case.
What expert evidence is and what it is for
Expert evidence consists of bringing into the proceedings the opinion of an expert — a forensic doctor, a forensic accountant, a ballistics specialist, an IT examiner, a valuer — on matters requiring scientific, technical or artistic knowledge beyond the judge's general culture. Its function is not to decide the case but to inform the court: the expert describes a method, applies it to certain data and draws conclusions, but the assessment of those conclusions always rests with the court.
Precisely because the court lacks the expert's knowledge, control of the report shifts towards the parties. It is they who, with their own experts and through questioning at trial, must test the soundness of the report: challenging the premises, the method used, the margins of error or the coherence of the conclusions. That adversarial testing is the guarantee of reliability of expert evidence, and it operates only if exercised at the right moment.
The provisional pleadings: the moment to disagree
The provisional pleadings (escrito de calificación provisional) are the document in which each party sets out its position before the hearing. They recount the facts, propose the legal classification, request the penalties and, what matters here, set out the evidence: that which each party proposes to take and the stance it adopts towards evidence already taken. This is the natural moment to announce that an expert report is being disputed.
A defence that does not share the expert report has several tools here: to express expressly its opposition or disagreement with the report, to request its clarification or expansion so that the expert can refine doubtful points, or to propose a party expert to provide a counter-opinion. What it cannot do is stay silent and reserve its objections for later: silence in the provisional pleadings about expert evidence already taken has a precise procedural meaning, which the Supreme Court develops in the decision discussed here.
Unchallenged expert evidence is deemed accepted
The core of the doctrine is this: where the accused party does not express in its provisional pleadings its opposition to or disagreement with the expert report already taken, nor request its clarification or expansion, that report acquires the character of established evidence, implicitly accepted and consented to. The absence of a challenge is not a neutral fact: it amounts to a tacit acceptance of the content and validity of the report.
The consequence is significant. Accepted expert evidence reaches the trial without contradiction over its validity and consolidates as incriminating evidence with full force. The court may assess it and ground its conviction on it without any formal objection weighing on the report, because the party that could have disputed it chose not to. This rule deprives no one of the right of defence; on the contrary, it presupposes that the defence had at its disposal the channel to challenge the evidence and did not use it: procedural burdens are exercised in their moment, and passivity has a cost.
The proper moment to object: the trial hearing
If the report reaches the hearing as accepted evidence, where are objections about the expert then ventilated? The Supreme Court's answer is clear: at the trial hearing, which is the proper setting for contradiction. There the expert appears, ratifies or explains the report and submits to questioning by the parties, who may ask about the method, the premises, the data used or the firmness of the conclusions.
Article 724 of the Criminal Procedure Act (LECrim) provides precisely that experts may be examined at trial, which makes the hearing the space where the reliability of the report is refined. Methodological shortcomings, doubts about the expert's qualifications or weaknesses in the conclusions are asserted there, through questions and, where appropriate, through contrast with a party expert. What is not admissible is to stay silent at that moment and raise those same criticisms for the first time at a later stage.
Why it cannot be challenged for the first time on cassation
Cassation is an extraordinary remedy that reviews the correct application of the law and respect for guarantees, not a second chance to reopen the debate over the evidence. That is why the Supreme Court rejects objections about the expert report being introduced for the first time on cassation: if they could and should have been raised at first instance — in the provisional pleadings and at the trial hearing — and were not, they arrive too late.
The reason is twofold. On the one hand, an unchallenged report has already consolidated as accepted evidence, so there is no actual breach to denounce: the party accepted the report. On the other, admitting new criticisms on cassation would break the rules of the procedural game and the principle of contradiction, because the expert could no longer respond to objections that were hidden when testifying. The doctrine thus protects the fairness of the process and the value of the proper moment.
The practical reading is sharp: the defence strategy regarding an expert report is decided at the start, not at the end. Anticipating whether the report will be disputed, announcing it in the provisional pleadings, preparing the questioning of the expert and, where appropriate, arranging a counter-opinion are decisions to be taken in their moment. Reserving them for cassation is not only ineffective: it leaves consolidated as incriminating evidence a report that might have been successfully contested at the proper stage. The case decided by the Supreme Court concerned a serious offence, but the lesson cuts across any proceedings in which expert evidence occupies a central place.
Frequently asked questions
What does it mean for expert evidence to be deemed accepted?expand_more
It means that, by not disputing the report at the prescribed procedural stage, the party has implicitly accepted its content and validity. The Supreme Court, in its judgment of 28 May 2026 (appeal 10709/2025), explains that an expert report not contradicted in the provisional pleadings, with no request for clarification or expansion, becomes established evidence. That tacit acceptance consolidates the report as incriminating evidence: it enters the trial with full evidential force, and late objections cannot diminish its value once the moment to dispute it has passed.
Why can I not challenge the expert report for the first time on cassation?expand_more
Because cassation is not the channel for introducing objections that could and should have been raised earlier. According to the Supreme Court, methodological shortcomings or doubts about the expert must be raised at the proper procedural stage, essentially the trial hearing, where the expert appears and can be questioned. If the defence stays silent in the provisional pleadings and at trial, those criticisms cannot be reserved for cassation: the report has already consolidated as accepted evidence, and the appeal arrives too late to dispute its validity.
What role do the provisional pleadings play?expand_more
The provisional pleadings (escrito de calificación provisional) are the document in which each party sets out its position before trial: the facts, the legal classification, the penalties and, above all, the evidence it proposes and the evidence it accepts or disputes. This is the natural moment to announce opposition to an expert report, to request its clarification or expansion, or to propose a counter-expert. The Supreme Court stresses that silence in this document about the expert evidence already taken has consequences: it is read as acceptance, so the report reaches trial without contradiction over its validity.
How should an expert report be challenged properly?expand_more
Challenging an expert report properly requires doing so in due time and form. In the provisional pleadings the defence must express its opposition or disagreement, request the clarification or expansion of the report and, where appropriate, propose a party expert. At the trial hearing it must question the expert on method, premises and conclusions, in line with Article 724 LECrim. Reserving the criticisms for a later stage, such as cassation, does not work: the Supreme Court recalls that a report not disputed in due time is deemed accepted and can no longer be contested.
Case law discussed
An expert report not challenged in the pleadings is deemed accepted
This analysis discusses a ruling of the Criminal Chamber of the Spanish Supreme Court. You can see its summary and full citation on our case-law page.
balanceView the ruling· Appeal 10709/2025arrow_forward