Computer counter-expertise

We can define a computer counter-expert, as a computer expert opinion that studies another computer expert opinion made by another expert, in order to detect errors. In short, it will search and examine in depth the methodology that has been used, trying to locate any error or failure, including also those things that have been overlooked in the analyzed report.

In order to be able to have a counter expert report, it is necessary to make a request to the corresponding judge by means of a model defense brief for the expert challenge. This is so because otherwise, by not making the challenge, it will be implied that we are satisfied with the expert’s report. In addition, it is necessary to consider the time limit to analyze a report, since, after a certain period of time, imposed by the court or due to the impossibility of analyzing the digital evidence again, nothing can be done.

It is important to know that this type of reports can give new possibilities to our lawyer. It gives new arguments and questions that can be the key to weaken the counter expert report.

Frequent cases

Among the most frequent reasons why a computer expert report can be challenged in defense brief, we will highlight the following:

  • Methodological: We must verify that the computer expert who made the original computer expert report complied with the forensic protocols, such as that the chain of custody was carried out in accordance with the law.
  • Practical: Verify that there have been no errors in the performance of the actions, for example, that the procedure used is objective and reproducible by another computer expert (preservation of the evidence).
  • Conclusive: Check that there has been no error in obtaining the conclusions, for example, obtaining a conclusion not based on an objective, practical and direct basis from the tests carried out. A common case is the lack of impartiality. Let us not forget that when dealing with reports that advocate for different parties, the expert may fall into the attempt to defend the indefensible influenced by his customer.
  • Qualification: Check that the alleged computer expert who made the expert opinion is collegiate and legally authorized.

Some interesting judgements

“After the Prosecutor’s Office was informed of this preliminary question, it referred that it was a matter of substance to be resolved in the sentence, regarding the sufficiency and purpose of the evidence. In his opinion, it was not possible to preserve and furthermore, at no time was the need for counterevidence announced by the defence, arguments that were shared by the other two private accusations. This argument was also reiterated in the report. The defence of the accused … stated that the prosecution said so in its qualification brief that it wanted to preserve, but it was not carried out.

“The legal resolution of the previous question raised requires to consider that effectively the preservation of the evidence and, more specifically, the lack of preservation of technological evidence will have repercussions at the time of the valuation of what is truly in the record without the due guarantees. The judge shares the fact that the lack of preservation has prevented knowing not only the authenticity of what was provided but also many other data, of relevance to the case, that could have redirected it in one sense or another.The lack of preservation of the server has prevented knowing who was the uploader that had placed the link on the mega server and had contributed it to the pages object of the proceedings, if it was any of the accused, whether or not the site actually had any automated way of inserting links once they were provided by contributors or uploaders, the programming of the site… etc.”

“Nor can such a plea succeed, inasmuch as it is up to the trial court to evaluate the evidence, and to record in the factual account the facts it deems accredited, and the fact is that it evaluated the counter expert report invoked by the appellant and states in its legal reasoning that the same, far from providing a technical and reasonable explanation of the allegations made, ‘is rather aimed at sowing doubts about the regularity of the collection of information prior to the COAS expert report, in short, to put this in question, alluding to the lack of guarantees in the chain of custody and in the collection of data from the technical director’s computer, as well as in trivial matters that do not succeed in undermining the validity and conclusions of the plaintiff’s expert report, whose procedural and technical correctness, on the contrary, is maintained in the other expert report of the defendant’. Therefore, having assessed said evidence by the judge a quo, and having underestimated the value of the Report whose conclusions, even interpreted by the appellant, are sought to be incorporated, we must reject the present ground of appeal.


This type of evidence can be contested and therefore, rejected, ruining the entire procedure. To determine whether this type of evidence can display probative value, the forensic analysis of a certified computer expert is essential.
Likewise, we must bear in mind that in recent years, the number of works and computer expert opinions that are dismissed in litigation and are not taken into account at the time of sentencing. The reason is none other than a huge increase in the number of computer experts who are not legally authorized to act before the courts, and who therefore incur in the crime of professional intrusion. We can find a clear example in the Judgment of the Superior Court of Justice of Madrid 531/2017, Social Chamber, Section 4, July 19th , 2017, in which it is stated in the first point of the grounds of law, that:

“The appealed ruling is essentially based on the ineffective and invalid expert evidence that has been provided as the only justification for the facts imputed in the letter of dismissal to the plaintiff, for several reasons explained by the Magistrate of Instance in her ruling. The first is because she understands that the expert presented by the company lacks an official degree in computer science, although at this point it is recognized that the expert is the person who provides computer assistance to the company as a freelancer, which implies at least a practical knowledge of what he is hired for. On the other hand, the informal nature of the expert evidence and the questioning of the chain of custody are argued. Special mention is also made of the breach of the guarantees of the plaintiff’s right to privacy at the time of carrying out the inspection and search of the computer equipment, declaring it proven that the plaintiff was not present. In short, the Magistrate of Instance, evaluating this evidence and the testimonies provided at the oral trial concludes that the defects in the practice of the expert evidence carried out by the company prevent granting probative value to this means of proof, and given that it is essential to prove the facts imputed to the plaintiff, declares the dismissal unjustified.”

The computer test must be certified in a computer expert opinion, prepared by a legally qualified computer expert. In our Frequently Asked Questions section you can find more information about it.

Why hire our services?

From FORENSICTECH we provide our clients with the security of having:

  • A computer expert specialized in your case, collegiate and legally authorized to act in the Spanish courts of justice.
  • Appropriate instruments and specialized software to develop your expert report.
  • Legally recognized chain of custody investigation and assurance methods.
  • An effective and efficient work in the requested expert report.
  • A certified computer expert opinion, which greatly increases your credibility and reliability before judicial bodies, as it is endorsed by a professional association.
  • A computer expert capable of facing the ratification in oral proceedings in all jurisdictional orders.
  • Our performance in all the courts of justice throughout Spain in all jurisdictional areas.


Receive the latest news by email
Remember that you can unsubscribe sending an email to
Skip to content