Forensic study of authenticity of audio recordings

Currently, technology is very present in our lives, so that more and more, computer-based evidence is part of everyday life in the judicial field. One of the most common cases is the accreditation or challenge of facts through audio recordings, in which it is sought to determine the origin, authenticity and integrity of the same.

Nowaday, audio recordings are available to everyone. Any mobile phone allows you to make an audio recording, which is very useful, by showing facts in an irrevocable way. But, we must bear in mind that an audio recording, given its nature, can be manipulated, so its mere hearing is not enough to prove its authenticity and integrity, being this objectionable, when added to the cause by mere transcription or collation by notary public.

As it is indicated in the Supreme Court Judgment 300/2015, May 19th , 2015 the proof of facts by means of audio recordings “… is approached with all caution by the courts of justice. The challenge of the same displaces the burden of proof on those who intend to take advantage of their probative suitability. In such a case, the practice of an expert evidence will be essential … “.

Frequent cases

The most frequent types of orders are:

  • Judge on the authenticity of an audio recording: Absence of manipulation, insertions or cuts.
  • Assess the presence of people in an audio recording: If there are several, if there is a third person in the scene, etc.
  • Identify the background of the recording: Know the environment in which it occurred.
  • Identify the speakers: Discard or prove the participation of a person in the recorded conversation.
  • Reconstruct scenes or events during a recording: Determine if there was violence, blows, falls, etc.
  • Recordings of child abuse: The conversation may have been erased and recovery is needed. In addition to certifying it, identifying the interlocutors and transcribing it.
  • Custody of minors: These are usually recordings where a parent says they want custody only for financial reasons, so as not to pay the pension for her children.
  • Domestic recordings in cases of gender violence: The non-manipulation and identification of the interlocutors must be clearly identified.
  • Labor Lawsuits: Where it is necessary to identify abusive causes at work, workplace bullying, insults, etc.
  • Recording of verbal contracts: Recordings where an agreement is reached and is not fulfilled.

Some interesting judgements

“… considering that there is an error in the evaluation of the evidence, since it is understood that the test carried out has not been correctly evaluated, since it has been based on a recording provided by the complainant. This recording was downloaded to his computer with the help of a friend, and later transferred to CD. Therefore, it is not certain that the recording has not been modified.

“The appeal is based on the fact that the recording provided at the hearing proves that it could have been manipulated by the complainant.

“The defendant attended the trial, assisted by a lawyer. Thus, the proceedings could have been accessed at all times prior to the hearing. Being able, in his case, to have challenged said recording, in order to have expert evidence, for verification or not, of the authorship by his client of the facts that were imputed to him. The judgment of Chamber II of the Supreme Court number 300/2015, May 19th, 2015, analyzes the question of the possibility of manipulating this type of evidence, concluding that this would imply the need to practice expert evidence, if it is contested, shifting the burden of proof to the party that intends to assert it. In this sentence, a detailed argument is made on the subject.”

“To this must be added the audio and video evidence practiced on the day of the oral hearing, although it was contested by the Defendant’s Defense for not having been subjected to technical expertise, both the copies of the WhatsApp, audio files and video, however the Chamber valued them in their fair measure.”


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.


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