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Evidence Collection & Forensics
This final episode of the ISACA Certified Information Systems Auditor (CISA) exam prep series covers the discipline of digital forensics and evidence collection. The episode examines the types of investigation an auditor may encounter, the distinct fields of computer forensics, the ordered steps of a forensic investigation, and the critical importance of chain of custody and disciplined evidence handling in ensuring that findings stand up in court.
What this episode covers
- Investigation types — administrative, criminal, civil, regulatory, industry-standards, and forensic investigations, and how the burden of proof and cooperation requirements differ across each.
- Computer forensics disciplines — database, email, mobile, memory, network, and malware forensics, and why different evidence lives in different places.
- Forensic investigation steps — the defined sequence from first response through expert witness testimony that protects evidence integrity at every stage.
- Auditor considerations during forensics — data protection, data acquisition to a controlled location, write-blocker use, volatile data capture, imaging, extraction, and two-audience reporting.
- Forensic techniques — deleted file recovery, reverse steganography, cross-drive analysis, live memory analysis, and stochastic forensics for insider-threat cases.
- Chain of custody — why the unbroken paper trail is what makes evidence admissible, and how a single careless action such as booting a device can permanently destroy it.
- Digital evidence handling — best practices for preventing contamination, using hash values, isolating mobile devices, and maintaining read-only access via write-blocking tools.
Watch the full episode above for the worked examples and detailed explanations of each concept.
Frequently Asked Questions
What are the main types of investigation and how do they differ?
An administrative investigation is internal and gathers facts so the right people can decide what action to take. A criminal investigation involves a suspected crime where guilt must be proven beyond a reasonable doubt and evidence may need to be shared with the defense. A civil investigation is a lawsuit where the bar is lower — a preponderance of evidence suffices. A regulatory investigation comes from an oversight body and requires cooperation, while a forensic investigation gathers evidence for court and is the most rigorous of all.
What are the steps of a forensic investigation?
A forensic investigation follows a defined sequence: first response, search and seizure of devices, evidence collection handled with great care, evidence security to prevent contamination, data acquisition, data analysis to turn raw data into real evidence, evidence assessment tying findings back to the incident, documentation and reporting, and finally expert witness testimony if the case goes to court. Every step is designed to protect the integrity of the evidence.
Why is the chain of custody critical in digital forensics?
The chain of custody documents who touched the evidence, when, and what they did with it — maintaining an unbroken paper trail. Any gap in the chain can cause the evidence to be thrown out in court. For example, booting a suspect computer causes the startup process to write to the drive, permanently altering the evidence, which is why specialists create an exact sector-by-sector copy first and always work on the copy rather than the original.
How should digital evidence be handled to keep it admissible?
Digital evidence must be handled by preventing contamination and never working on the original device — always image first and work on the copy. Hash values should be used to detect any tampering, since a changed hash proves the evidence was altered. Mobile devices should be placed in airplane mode inside a shielded bag to block remote wipes or stray signals, and the device power state should not be changed — if it is on, leave it on, to preserve volatile memory.
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Reference: This article is based on concepts discussed in Evidence Collection & Forensics.