The Digital Footprint: Using Digital Data in Criminal Investigations
Passionately developing careers.

IT Management Blogs

The Digital Footprint: Using Digital Data in Criminal Investigations

  Jan 22 2019

# IT Management

Over the years, I have written multiple articles on the subject of digital or cyber forensics and the importance it serves in supporting the modern world with regard to corporate and government incident response, first responder engagements, and more general aspects of scene-of-crime management in the digital age.

Before we get into the detail, please allow me to travel back to my days in the Royal Air Force, during which I took training on the subject of crime scene management. We covered a variety of issues, including the importance of preserving life, accessing the scene, ensuring that any acquired artifacts were properly documented, as well as how crucial it is to keep a contemporaneous record that one can present to any enquiring and challenging authority.

Following these practical gems of knowledge, I transitioned them over to the operational world of policing, dealing with cases ranging from the RTA-72 (drinking and drive), administering the breath test, overseeing the obtaining of blood samples, right to the world of counter intelligence, which included, conducting searches of persons and premises which were suspected to be the clandestine and unauthorized location for the illicit storage of high-grade classified materials. However, no matter the engagement, the same rules were always applied on every occasion in the form of a ‘process’; the King (and Queen) to assure that the investigation, and supporting acquired artifacts were robust, defensible (if subject to challenge) and that an accurate and robust chain of-handling/custody along with secure storage/ transmission, had been applied at all stages.

Note: No matter what actions have been taken, what has been acquired, and what the implied burden of proof is, if the process is broken, it can (and will) serve as the ‘Achilles Heel’ to challenge and diminish the value of what is presented, seeking to make it inadmissible, or to reduce its weighting to the case.

In essence, over the years, the very foundation of scene-of-crime management has not really changed, apart from one exception, which arrived in the guise of the ‘Digital Footprint’ (‘DF’).

The Digital Footprint

Here we are looking into the era of technology, people with tilted heads, walking down the street staring into the palm of their hand, the quick-jerk fingers of the lady on the train as she complies a text manage or email, right down to the case of the Soham Murders of Holly Marie Wells and Jessica Aimee Chapman in 2003 committed by Ian Huntley – all of which have one thing in common: The Digital Footprint (‘DF’).

In the case of the Soham murders, the presence of the ‘DF’ was one key area of evidence supporting the prosecution. Whilst Huntley denied being in the vicinity of the crime, his cell phone inferred a different story as it had registered in, or close to the edge of the radio-cell, and thus played an important part in placing and inferring that the suspect’s cell phone (and by association Huntley) had been close to, or in attendance at the scene

Extrapolate this forward to 2015, with Location Services and GPRS facilities, which can track and place individuals to locations, and we can start to appreciate the implications of what the ‘DF’ can present. We may also look to some of low-cost tools, which have emerged to track individuals, and place them to a certain physical location – that is, assuming the transmitting device is in the possession of the legitimate owner. One such tool is Echosec.

In our technological age, it may therefore be argued that around 99.99% of scenes-of-crime are associated with some form of technical component, and by implication it follows that there is a close proximity, or a presence of the digital footprint in existence.

For example, the last phone call made by a victim or an attacker, a social media search, some form of conjoined electronic interface between suspects; use of a home or office-based VoIP appliance; metadata hidden deep inside the code of an image or document, the contents of a removable media, or a computer hard drive, CCTV, and not forgetting the prospect of any related artifacts, which may be resident within the circuits and storage of on-board automobile computing facilities – all possess unknown possibilities for the representation of ‘DF’.

It is for this reason I put the case forward that, whilst on rare occasion the ‘DF’ element may not be relevant at the end of the investigation, it must be considered as a matter of priority within the first responder landscape, and should thus be accounted as a process line entry as a matter of course for every crime scene or subsequent investigation encountered.

Locard’s Exchange Principle

When considering the digital artifact, Locard’s Exchange Principle is equally applicable to the world of bits and bytes in that the perpetrator of a crime will bring something into the crime scene and leave with something from it. For instance, consider the following as applicable to a digital footprint:

“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fiber from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, and it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.”

Here, it is also important when considering digital forensics not to suffer tunnel vision on the digital element only, as the physical nature of the artifact may also provide proof of the act in both mens rea (guilty state of mind), and actus reus (the act).

Robustness of Standards

Given the importance of this digital science, it may be asserted that it cannot be left any longer to an approach based on chance, best endeavors, or a have-a-go approach, as the resulting implications and the prospective impact(s) on both investigator and suspect carry the potential of real world impact which could manifest in woeful, damaging, and life changing implications. For instance, take the case of an ‘expert witness’ who provided testimony in support of the prosecution in a case of medical malpractice which focused on a key email artifact. However, our expert in this instance only passed judgment on what could be seen as lexical content within the body of the communication, and took the ‘To’ and ‘From’ as prima facie facts, and did not follow through with any further corroboration of the email headers – leaving the interpretation and assessment of the acquired artifact open to error – something which should have been subject to challenge.

ISO/IEC 17025:2005

It is for this reason why the application of the ISO/IEC 17025:2005 is so very important to drive the intrinsic expectations of competence, experience, and skill to assure that professionals who are engaging in this scientific practice meet the expectations of the discipline.

For example:

  • Was the digital evidence tainted or compromised regarding how it was collected and where it was stored?
  • Is the chain-of-custody complete and accurate?
  • Is on-the-job training alone sufficient to qualify the examiner as an expert?
  • Are documented, verified and validated procedures available for review?
  • Is the case file documentation complete and detailed such that another examiner can recreate the results of the examination(s)?
  • Were the examination results peer reviewed?
  • Is the examiner competent to perform the examination(s)?
  • Was the examiner’s proficiency tested?
  • How are the forensic computers and forensic software maintained and updated?
  • Are the software tools used legitimate, licensed, authorized versions?
  • Were the software tools performance tested prior to their use?
  • Did the software or hardware alter or change the original digital evidence?
  • Were scientific principles followed during the examination(s)?

Hardware, Applications and Tools

When it comes to the hardware and applications in support of the digital forensic mission, whilst home-grown systems may well provision a level of service, they may not be of a proven ability, or accepted as trusted instruments to support the criticality of a serious investigation. Thus choosing established, and proven tools from the stables of access data in the form of FTK, EnCase, or the cost effective solutions from Paraben can go a long way to satisfying the provision of robust solutions – with the caveats that:

  • They are maintained with the most current updates
  • They are in the hands of proficient, and trained operators

There is, of course, the need to support the operational service of our digital forensics first responders with specialist hardware, such as write-blockers like the UltraBlock device to assure that when using Wintel Systems, the target drive is not contaminated with any anticipated ‘are-you there’ system calls, which can leave their invasive footprint on the artifacts(s) under investigation

For the first responder working in the field, it is important to assure the collected evidential materials are afforded a commensurate level of protection when outside of any controlled environment. A very versatile and low-cost tool I have seen deployed is the CESG CCTM, FIPS 140/2 IStorage USB drive, fully enabled with Pin-Pad Access Control.

The above is not a fully comprehensive list but does hopefully provide some exposure to the type of tools, applications and investigative support with which the digital forensics operator needs provisioning with.

Fit for Purpose Operations

It may be that some organizations consider the gravitas which is applied to the technological requirements of such a critical service to be beyond the internal capabilities and resources of the internal team, and that running a fully blown and robust internal digital forensics team within a commercial organization may be cost prohibitive, and not represent a solid investment or ROI (Return on Investment). However, this should not bar any company from provisioning an in-house first responder capability (FRC) in the form of a first touch, first response/engagement element whilst at the same time recognizing the implied limitations of the team.

So, here, one may consider:

  • Creation of policies to cover the objectives of the service offering.
  • Establish processes which may be applied to support the first responder engagement.
  • Define clear Terms of Reference (TORs) for the first responder team.
  • Provision an adequate base level of training to underpin their areas of anticipated expertise and responsibilities.
  • Recognize limitations
  • Have an established contract in place with an external professional provider of such a service.


It is an established opinion of many professionals, practitioners and academics that to provision such a service as digital forensics, by inference dictates the necessity exists to grant a high level of autonomy to those who are responsible, and incumbent to support such professional expectations. We must also keep a clear mind on one important fact: to acquire what can be dynamic and intangible, and time sensitive artifacts in the early stages of an investigation presents of highest opportunity of success.

However to return to a scene which has seen the reuse, or change of state of any artifacts may well encounter they are no longer present, or have been corrupted, and diminished in their evidential value. As with dynamic states, they do not always wait for tide or mankind to return to acquire what was missed at the first pass.

About the Author


John is a leading expert in the field of Cyber-Security. With over 30 years of international experience, he is a World Class Info-Crime, Cyber Security Researcher who has worked within the Covert Worlds of CESG, GCHQ, ‘TK’ Sky Technology, with the Security Services. He has delivered over 90 Global Presentations, and has originated over 100 Papers, & Articles on Cyber-Security.

He is actively involved with supporting the countering of eCrime, eFraud, and on-line Child Abuse, an ENISA CEI Listed Expert and an Editorial Member of the Cyber Security Research Institute (CRSI). John is a Fellow of the British Computer Society (BCS), Fellow of the Royal Society of the Arts (RSA), Board Advisor to the Digital Trust and Writer for SC Magazine UK. He was the Originator of DarkWeb Threat Intelligence, CSIRT, Attack Remediation and Cyber Training Service/Platform, Accreditation Assessor and Academic Practitioner and Accredited Advisor to the Chartered Society of Forensic Sciences in the area of Digital/Cyber Forensics.

John is also a practicing Expert Witness in the area of IT, and the originator, and author of a CPD/MSc Module covering Digital Forensics, and Investigations.

Professor John Walker is a Visiting Professor at the School of Computing and Informatics, Nottingham Trent University (NTU), Visiting Professor/Lecturer at the University of Slavonia, CEO of HEXFORENSICS LTD, and Independent Consultant in the arena of IT Security and Forensics, and Security Analytics.