Digital evidence in criminal matters: the validity of WhatsApp, emails and social media
The way we communicate has changed radically, and criminal proceedings have had to adapt. Today the relevant conversations occur on WhatsApp, in emails or on social media, and digital evidence has become the main battlefield of many proceedings. But this evidence poses challenges that traditional evidence does not: how to establish that a message is authentic, under what conditions the police can access a phone, what validity a screenshot has.
Digital evidence is any information stored or transmitted in digital format that is relevant to the process: instant-messaging messages, emails, posts and messages on social media, call logs, photographs and videos, geolocation data, browsing history or digital transactions. All these types have in common that they are easily manipulable and difficult to authenticate.
Obtaining it affects fundamental rights that limit how it can be acquired. The secrecy of communications, under Article 18.3 of the Constitution, protects digital communications with the same intensity as telephone ones; their interception requires judicial authorisation. The right to privacy, under Article 18.1, protects the content of the phone, one of the richest repositories of private information. And data protection regulations add a further layer. Ignoring these limits results in the nullity of the evidence.
Digital evidence is validly obtained through judicial authorisation, by way of a reasoned and delimited order; with the free and informed consent of the holder; or when the victim themselves provides the communications in which they were a party.
The most vulnerable point is authenticity: digital evidence can be manipulated with accessible tools. That is why the Supreme Court has established that a simple screenshot is not enough to establish the authenticity of a message. For digital evidence to have full value, it is advisable to have a notarial record of the content, a computer expert report certifying that it has not been manipulated, the direct judicial obtaining of the device with a chain of custody, or certification from the service provider.
On WhatsApp messages, the Supreme Court has established that they are admissible as documentary evidence, that their authenticity is not presumed and must be established, and that computer expertise is the most solid means for this. Emails present favourable particularities, because providers keep records on their servers and can certify authenticity; their metadata is relevant but also manipulable. On social media, posts on public profiles can be documented freely, while private profiles and direct messages require the same guarantees as any private communication; it is advisable to act quickly to preserve the content, because it may be deleted.
Faced with the prosecution's digital evidence, the defence may challenge the legality of how it was obtained, question the authenticity of the content by requiring computer expertise, question the chain of custody of the device and, where appropriate, contextualise the messages to offer a different interpretation. It is one of the areas where procedural strategy can make the greatest difference to the outcome.
