How Digital Evidence Is Tested and Challenged in Criminal Trials in Western Australia

Criminal investigations are increasingly driven by data collection and digital technologies.

Modern lives are monitored by digital devices.

Whether it is smartphones recording our communications and movements, vehicles storing GPS data or social media capturing our random thoughts and observations.

As a result, digital evidence commonly appears in criminal matters, whether to corroborate witness accounts, contradict alibis, or establish patterns of behaviour.

The following explains how digital evidence is collected, tested and challenged in criminal trials in Western Australia and how legislation and case law shape its admissibility.

Types of Digital Evidence Commonly Used

There are a variety of types of digital evidence that are commonly utilised in criminal trials.

Phone data is among the most frequently relied upon forms of digital evidence, with prosecutors often using SMS and messaging app communications, call logs showing contact between parties and voicemail recordings as part of evidence.

Social media posts, private messages and images are also regularly tendered in court to prove admissions of guilt, the making of threats, associations between parties and location data.

Metadata can be sourced from digital devices to establish information about the time and date data was created, its modification history and device identifiers.

Finally, CCTV footage is common in most private premises, with its extraction providing evidence to identify suspects, capture offenders, or confirm the timing of events.

How Digital Evidence Is Collected

Under most circumstances, police will obtain a search warrant to search and seize devices containing digital evidence.

Search warrants must be lawfully issued.

If a warrant is invalid or improperly executed, the admissibility of resulting evidence may be challenged.

Once devices are seized, forensic extraction tools are used to retrieve data, including deleted messages, call history, application data and internet browsing history.

It’s important throughout this process that the chain of custody is maintained.

The chain of custody refers to the documented handling of evidence from seizure to presentation in court.

Breaks in the chain may raise doubts about whether data was altered, whether it came from particular devices or was otherwise contaminated.

Testing the Reliability of Digital Evidence

Digital evidence may be tested by the defence in a criminal trial based on its being unreliable or otherwise inadmissible.

Digital files can be edited, altered or fabricated.

Screenshots may be manipulated.

Messages may be selectively presented without context.

The prosecution must establish the origin of the data, that it has not been altered and how it is interpreted.

The defence could challenge all of this.

Further, data will need to be authenticated by forensic experts, whom the defence may cross-examine.

Legal Challenges to Digital Evidence

Digital evidence may be excluded from a criminal trial if it has been obtained improperly or unlawfully, or if its admission would compromise the fairness of the trial.

In Bunning v Cross (1978) 141 CLR 54, the High Court states that in relation to unlawful or otherwise improperly obtained evidence, courts must balance the seriousness of the impropriety against the public interest in admitting reliable evidence.

If police exceed the scope of a warrant or conduct an unlawful search, exclusion of the evidence may be sought by the defence.

Further, if digital evidence is misleading, incomplete or obtained in circumstances undermining reliability, exclusion could be argued.

The Role of Expert Evidence

Digital evidence is often technical, as such courts rely on forensic IT specialist witnesses to explain how data was extracted, the reliability of the data and the limitations of forensic tools.

Expert opinion is admissible where it is based on specialised knowledge derived from training, study or experience.

However, evidence will be inadmissible if a person lacks sufficient specialised knowledge or moves beyond their expertise.

A defence can cross-examine forensic IT specialists as to their qualifications and methodology, as well as provide alternative experts who may challenge certain interpretations of digital evidence.

Digital Evidence and the Standard of Proof

Prosecutors must prove an offence in criminal trials to the standard of ‘beyond a reasonable doubt’.

Even if compelling, where digital evidence is solely relied upon by the prosecution to prove a charge, it must be sufficient to prove each element of an offence to meet this criminal standard.

Digital evidence may still leave room for reasonable doubt if it is ambiguous, lacks context or relies on questionable interpretations.

Issues may also arise if there are gaps in the chain of custody or if questions are raised regarding the reliability of the data extraction.

Even where digital material has been extracted and interpreted correctly, it may be insufficient to establish the elements of an offence beyond a reasonable doubt if its connection to the accused’s alleged guilt is not firmly established.

Get Legal Advice

In modern criminal trials, digital material may be powerful, but it is not decisive merely because it is ‘techy’.

Careful legal scrutiny remains essential to ensure fairness and accuracy in the administration of justice.

If you are facing a criminal matter in Western Australia, it is essential to seek guidance from an experienced Perth criminal lawyer who can provide expert advice, protect your rights, and help achieve the best possible outcome for your case.