How much weight does ones own expertise carry compared to that of a court expert in criminal cases?

In criminal proceedings, and certainly in sexual offenses cases, expert reports often play a decisive role. But what if you disagree with the court expert and engage a private expert yourself? As a rule, the criminal court judge has the final say on the evidential value of the reports submitted to him. A judge may base his or her opinion on the court expert and disregard the report of your own expert, as long as he or she gives reasons for doing so and you have had the opportunity to challenge this.

The facts and context

This issue was recently discussed in a ruling of the Court of Cassation of 25 November 2025. The case revolved around serious sexual offenses, including the rape and indecent assault of a minor under the age of ten.

During the investigation, a forensic expert (Dr. T.) was appointed to assess the credibility of the statements made by the minor victim during the audiovisual interview. The defendant disagreed with the conclusions of this forensic expert and engaged a counter-expert (Dr. D.).

This expert came to very different conclusions and stated that the verdict would have been different if his report had been followed. The defendant argued that his right to a fair trial and the right to adversarial proceedings had been violated because the court of appeal had disregarded the findings of his own expert in favor of the court expert.

In addition, the defendant was also prosecuted for possession of images of sexual abuse of minors. He claimed that he had downloaded these images “accidentally” and that the search term “teen sex” did not necessarily indicate an intention to search for child pornography.

The decision of the Court of Cassation.

The Court of Cassation rejected the defendant's appeal and upheld the principles governing the assessment of evidence.

The decision is based on the following pillars:

• Freedom of the judge: When the law does not prescribe specific means of evidence, the judge has sole discretion to assess the facts. This also includes weighing up the report of a court expert against that of the defendant's own expert.
• No violation of fair trial: The mere fact that a judge bases his decision on the court expert's opinion and not on the counter-expertise does not constitute a violation of the right of defense. However, this is conditional on the parties having been able to contest these documents.
• Motivation is crucial: In this case, the court of appeal explained why it did not follow the private expert's opinion: his analysis did not comply with internationally recognized guidelines (CBCA) and lacked a validity check.
• Proof of intent in digital crimes: The Court ruled that the use of the search term “teen sex” could indeed indicate a deliberate search for images of minors. The number of images (36) made the defense of “accidental catch” implausible.

Legal analysis and interpretation

This ruling confirms the case law on the free assessment of evidence in criminal cases. It is a misconception that a “counter-expertise” automatically neutralizes the probative value of a court expert.

The hierarchy of experts

Legally speaking, there is no formal hierarchy, but in practice, the court expert often enjoys greater authority because they act on behalf of the court and are considered to be independent. A private expert, on the other hand, is paid by one party, which can create the perception of bias.

However, the Court of Cassation clarifies that the right to adversarial proceedings (Article 6 of the ECHR) does not mean that the judge must follow the defense's view. The right to adversarial proceedings means that the defense must have the opportunity to:

1. Take note of the file;
2. To discuss the evidence;
3. To submit counterevidence (such as a counterreport).

As long as the judge does not ignore the counter-report but explains in his judgment why he is not following it (for example, by pointing out methodological flaws such as the lack of an SVA validity check in sexual abuse cases), the decision is legally watertight.

Intent in possession of prohibited images

Also interesting is the interpretation of Article 417/46 of the Criminal Code (formerly 383bis CC). The “knowing and willing” possession of images is required for criminal liability. The Court confirms that judges may infer intent from external circumstances, such as specific search terms. The term “teen sex” was interpreted here by the trial court as an indication that the person was specifically searching for minors, and not for regular adult pornography.

What this specifically means

This case law has consequences for various parties involved in criminal proceedings:

• For the defendant: Engaging a private expert is useful, but no guarantee of success. It is crucial that your private expert applies the same strict methodological standards as the court expert. In sexual abuse cases, analyses must comply with CBCA (Criteria-Based Content Analysis) guidelines. A report that merely expresses a different opinion without scientific substantiation will be dismissed by the court.
• For victims: The credibility of your statement is key. If a court expert assesses your statement as reliable, a perpetrator cannot simply undermine it with a one-sided report, as long as the initial assessment was carried out in a methodologically correct manner.
• In the case of cybercrime: Be aware that search history and search terms are used as hard evidence of ‘intent.’ The defense that images ended up on the computer “accidentally” (“bycatch”) is rarely accepted when search terms such as “teen sex” are found in combination with a significant number of files.

FAQ: Frequently Asked Questions

Is the judge obliged to appoint a new expert if two experts contradict each other?
No. The judge has sole discretion. He may decide that the court expert's report is sufficiently convincing and reject the counter-report, as long as he provides reasons for doing so.

Will a procedural error in the cassation brief have an impact on my case?
Not always. In this judgment, the Court ruled that the absence of the attorneys's accreditation number on the brief is not grounds for inadmissibility, as long as the attorney does have the required certificate. However, serving a brief on the other party at the wrong address does lead to inadmissibility with regard to that specific party (see Article 429 of the Code of Criminal Procedure).

Is searching for “teen sex” a crime?
A search term in itself is not a criminal offense, but it can serve as evidence of intent (malice aforethought) to possess criminal material (images of sexual abuse of minors). The judge can infer from this that you knew what you were looking for and that the possession of the images was not accidental.

Conclusion

Refuting a court expert requires more than just a conflicting opinion; it requires a methodologically flawless counter-report. In Belgium, the criminal court retains the final say in the assessment of evidence.