Updated to LO 1/2026 and LO 1/2025 · Reviewed July 2026 · Author: Francisco Javier Martín Porras, criminal lawyer and court expert · SCJE team
When the judge needs scientific or technical knowledge, the expert enters: forensic doctor, computer forensics specialist, handwriting examiner, accountant. Their report guides entire investigations and decides trials, but it is not sacred word: it is contrasted, the expert is challenged for cause or discredited, and the report is subjected to adversarial examination. As a firm with its own expert laboratory, we litigate expert evidence from both sides: proposing it and dismantling it.
In brief. In brief. The judge orders the expert examination of their own motion or at a party’s request during the investigation (art. 456 LECrim). The parties may appoint their own expert to take part in the proceeding (art. 471). The court-appointed expert is challenged for fixed causes; the party expert is discredited at trial. At the trial hearing the report is ratified and subjected to adversarial examination (art. 724).
When knowing or assessing a fact requires scientific or artistic knowledge, the judge orders an expert report (art. 456 LECrim), of their own motion or at a party’s request. The report guides entire investigations and decides trials, but it is not sacred word: the court-appointed expert can be challenged for fixed causes, the opposing party expert can be discredited at trial, and every report is subjected to adversarial examination at the hearing (arts. 723 to 725 LECrim).
As a firm with its own expert laboratory, we litigate expert evidence from both sides. Our method: early appointment of a party expert to take part in imagings and analyses (art. 471), second expert opinions on official reports reviewing methodology and conclusions, challenge for interest or relationship and discrediting that degrades credibility, and technical cross-examination of the adverse expert on method, margin of error and chain of custody.
| Stage | Legal basis | Content | Defence opportunity |
|---|---|---|---|
| Ordering the expert report | Art. 456 LECrim | Scientific or artistic knowledge needed to assess a fact | Delimit the remit in writing; the question defines the value |
| Classes of experts | Art. 457 LECrim | Titled or untitled experts | The difference weighs in the assessment of the report |
| Number and appointment | Arts. 459 and 460 LECrim | Two experts in the sumario, one in the abbreviated; notified appointment | Lack of notification with unrepeatable analysis: material lack of defence |
| Challenge for cause | Arts. 468 to 470 LECrim | Kinship, interest in the case, manifest friendship or enmity | Raised before the report; removed expert |
| Party expert | Art. 471 LECrim | Takes part in the proceeding, observes and places remarks on record | Witnessing acquisitions avoids disputes over hashes and custody |
| Practice of the report | Arts. 474 to 483 LECrim | Object, operations and conclusions; expandable in statement | All three parts are attacked: object, method and conclusions |
| Trial hearing | Arts. 723 to 725 LECrim | Ratification and adversarial examination of the report | Technical cross-examination on method, error margin and custody |
| Documented expert reports | Consolidated case law | Unchallenged analyses may be assessed as documentary evidence | Express challenge forces the expert to appear at trial |
Summary drawn from the Spanish source page for orientation purposes. The applicable provisions are those in force at the relevant time; each case requires individual analysis by a criminal lawyer.
Original commentary by the firm, checked against the reference work in our library: Ley de Enjuiciamiento Criminal Comentada, Lefebvre-El Derecho, 13th edition, May 2026. Reports fall more often for their method than for their result: technical equality of arms exists if it is exercised, and our own laboratory issues reports and second opinions in computer forensics, handwriting examination and other specialties.
It is attacked through three cumulative routes: challenge or discrediting of the expert, counter-expertise confronting method and conclusions, and technical cross-examination at the hearing on margin of error, standards and chain of custody.
The party expert of art. 471 LECrim may witness the acquisition: it avoids later disputes over hashes and chains of custody, and its unjustified denial vitiates the proceeding.
The express challenge of documented reports (drug analyses, valuations) costs one line and forces the prosecution to bring the expert to the courtroom, opening the adversarial examination.
Our laboratory issues reports and second opinions in computer forensics, handwriting examination and other specialties: technical equality of arms exists if it is exercised.
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Société de Conseil Juridique et Expert es un despacho de abogados con sedes en Madrid, Alicante, Londres y París, especializado en defensa y acusación penal, delitos económicos y corporativos y derecho tecnológico. Trabajamos con orientación estratégica en procedimientos penales complejos, propiedad intelectual y análisis forense avanzado, y prestamos consultoría jurídica, compliance y escudos de protección a particulares y empresas. Atendemos desde Alicante y Madrid, con consulta online en toda España y asistencia al detenido 24 horas. Resuelva sus dudas en las preguntas frecuentes o solicite una primera consulta.
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