Why Are Digital Forensics Expert Reports Rejected in Court? A Pattern Analysis of Supreme Court Rulings

A digital forensics expert report is the technical document that allows digital evidence to carry meaning in a trial. Yet not every expert report is accepted by Turkish courts. When a judge finds a report insufficient, incomplete, or methodologically flawed, the judge does not base the verdict on it; sometimes a supplementary report is requested, sometimes a new expert is appointed for re-examination, and sometimes the report is disregarded entirely. A look at the Court of Cassation's reversal rulings shows that certain rejection patterns appear again and again.

This article addresses why digital forensics expert reports are rejected in court, the recurring patterns found in the Court of Cassation's publicly available case search system, and the methodology a report must follow to stand. The content is a continuation of the DSET digital forensics process article and complements the foundational information on the structure of an expert report.

How an Expert Report Reaches the Court

In civil proceedings, the authority to appoint an expert is regulated under Article 266 and the following articles of Law No. 6100, the Code of Civil Procedure. In criminal proceedings, an expert is assigned within the framework of Articles 62 to 73 of Law No. 5271, the Code of Criminal Procedure. Under both procedures, the judge or the public prosecutor appoints an expert in matters whose resolution requires technical knowledge.

The appointment decision sets out the expert's duty, the questions to be answered, and the delivery deadline. The expert examines the file, inspects the digital materials, takes measurements, records findings in a written report, and submits it to the court. Delivering the report to the court is not sufficient on its own; for the report to acquire evidentiary value, the judge must find it adequate, it must withstand the objections of the parties, and where necessary it must be reinforced by a supplementary or root report.

This is precisely where the trouble begins. Digital forensics is a technical field the judge does not directly observe. Every sentence of the report must be transparent, traceable, and reproducible. In the reversal grounds that can be reviewed through the Court of Cassation's public Case Search system, the common reasons for a report's rejection settle into recognizable patterns. Below, these patterns are grouped into ten main categories.

1. A Broken Chain of Custody

The chain of custody is the uninterrupted record showing who held the digital material, when, and under what conditions, from the moment it was seized to the moment it was presented to the court. In Turkish practice it is also referred to as the "preservation chain," the "chain of custody," or the "chain of seizure reports." In international standards, ISO/IEC 27037 regulates this chain under the heading "identification, collection, acquisition, and preservation of digital evidence."

When the chain is broken, the report cannot guarantee that the data analyzed truly came from the material that is the subject of the case. A frequently seen pattern in Court of Cassation rulings is that, because there is no documentation of where the material was kept, who accessed it, and under what conditions it was stored from seizure to the examination date, the report cannot serve as the basis for the verdict. In a typical scenario, the material is taken from the law enforcement unit to the evidence depot, handed over from there to the expertise unit, and kept in custody after the examination; but if, at each of these steps, the identity of the person receiving and the person delivering the material, the seal status of the safe in which it was stored, and the seal number have not been documented, the chain is deemed broken.

Another typical problem is the material waiting for a long time in "cold storage" on a law enforcement shelf, with conditions such as temperature, humidity, and magnetic fields going unrecorded during that wait. Data on disks and memory cards is affected by the physical environment. When the report does not state under what conditions the material was stored, the expert's assertion that the data in hand is "unaltered data" is weakened.

How to prevent it: From the moment of seizure, the record templates specified in ISO/IEC 27037 and the guides of the Department of Expert Witnesses should be used; every receipt and handover step should be logged with the date, time, the person's signature, and a hash value. The safe or evidence room where the material is stored should be sealed, re-sealed with a new seal at each opening, and the seal numbers should be recorded in the report.

2. Failure to Compute or Verify the Hash Value

The lifeblood of digital forensics methodology is the cryptographic digest (hash) value computed after imaging the digital material. Computed with the MD5, SHA-1, or preferably SHA-256 algorithms, this value mathematically proves that the material did not change during the examination. Because academic collision attacks have been demonstrated against the MD5 and SHA-1 algorithms, current practice favors SHA-256 and SHA-512.

A recurring ground in Court of Cassation rulings is that the report is not auditable because the expert did not compute the hash value of the original digital material, did not work on an image, or did not present the hash value added to the report in a verifiable form. With no hash, no one can prove that the file the report references is genuinely that file. When there is no hash, the expert saying "the examination was performed on the original material" carries no technical guarantee.

Another recurring pattern is computing the hash value only at the moment of imaging and not re-verifying it after the examination is complete. In digital forensics methodology, the hash must be verified at no fewer than two points: after imaging and before the report is delivered. The fact that the same value can be reproduced is the mathematical proof that the material did not change at all during the examination.

How to prevent it: When imaging the material, separate SHA-256 values should be computed for the source and the target, recorded in the report, attached as an appendix, and re-verified at the end of the examination. Formats that provide internal verification, such as the Expert Witness Format (E01) or the Advanced Forensic Format (AFF), should be preferred for imaging; if a raw (dd / raw) image is used, the hash file should be preserved separately. This point is also clearly regulated in the NIST SP 800-86 Computer Forensics Guide and the SWGDE Best Practices documents.

3. Failure to Use a Write Blocker

During imaging, connecting the disk attached to a computer in a writable state can change the timestamp of even a single file on it. Modern operating systems may perform background writes to access the cache of connected disks; even without the user's awareness, this alters metadata fields such as the disk's "last accessed time." This breaks the integrity of the evidence. A write blocker, in either the hardware or software layer, ensures the disk is read-only.

One of the patterns that reaches the Court of Cassation is the absence of an explicit statement in the report that a write blocker was used during imaging. This omission removes the assurance that the digital evidence was unaltered at the moment of contact, and the report is assessed as "methodologically insufficient." In some cases, even if the expert verbally states that a write blocker was used, the court cannot verify this assertion because the information does not appear in the body of the report.

In mobile device examinations, a hardware-based write blocker is not always applicable; in such cases, software-based protection is used (for example, the read-only mode of Cellebrite UFED, careful sequencing of ADB commands, or sector-level reading in JTAG/ISP mode). Whichever method is chosen, the report must explain why and how that method was applied.

How to prevent it: In the "tools used and methodology" section of the report, the brand, model, serial number, and verification test of the write blocker should be clearly stated; where possible, a photographed accessory log should be added. The model information of hardware-based write blockers such as Tableau, WiebeTech, or CRU should be stated along with the compatible disk interface (SATA, SAS, NVMe, IDE, USB).

4. Leaving the Methodology Undefined

An expert report must be reproducible, such that another expert approaching the same data with the same steps would reach a similar result. This is the fundamental principle of the scientific method.

Another recurring pattern seen at the Court of Cassation is the expert saying "I conducted the examination and reached this conclusion" but not showing which tool, which version, which query, or which parameters were used. If the methodology is undefined, the report cannot be audited. A judge does not base a verdict on a report that cannot be audited.

How to prevent it: The report should separately include the sections "tools used" (for example, EnCase 21.x, FTK Imager 4.7, Autopsy 4.20, Cellebrite UFED 7.x, X-Ways Forensics), "method applied" (imaging, hash verification, file system analysis, slack space scanning, timeline extraction), "steps followed," and "raw data obtained." The preferred approach is to document, in an appendix, the query used for each finding (for example, a SQL statement, a grep command, an EnCase EnScript module). This approach makes it possible for another expert to reach the same result with the same query and lifts the methodology out of being a "black box."

5. Making Legal Interpretations (Exceeding the Scope of Duty)

An expert answers a technical question with a technical answer. Legal characterization is the exclusive domain of the judge. If an expert report includes statements such as "the defendant is guilty," "this message contains a threat," or "the act bears the elements of fraud," the expert has exceeded the limits of their authority. This boundary matters both for procedural economy and for protecting the judge's discretionary power.

Both HMK Article 279/4 and CMK Article 67 establish that an expert may not make a legal assessment. In Court of Cassation rulings, the rejection of a report on the grounds that the expert made an "evidentiary assessment," "interpreted the facts," or "expressed an opinion on whether the act constitutes a crime" is a frequently encountered pattern. The expert's task is not to take the place of the judge but to build a technical bridge that allows the judge to reach a decision.

To give a practical example, the question of whether a WhatsApp conversation "contains a threat" is a legal question and lies outside the expert's field of duty. By contrast, the questions "in which WhatsApp database table is this message located, what is the message's timestamp, was the message deleted, and if deleted, by what method was it recovered" are technical questions and fall within the expert's domain. Confusing these two categories is one of the most frequent reasons a report is rejected.

How to prevent it: The report should be limited to factual technical findings such as "this file existed on this device," "this message was sent on this date," or "this IP address connected within this time interval." Interpretation, discretion, and the characterization of a crime should be left to the judge. The expert should place a standard closing sentence at the end of the report along the lines of "the findings made are technical in nature; the legal assessment lies within the discretion of the court."

6. Unsourced Findings (Presenting a Conclusion Without Showing the Path of Data Extraction)

When a report states "this file was deleted and recovered," it must specify which tool the recovery was performed with, which sector it was read from, and how the MFT or $LogFile records were interpreted.

A striking pattern in Court of Cassation rulings is the expert saying "this deleted record was found" but not presenting the technical proof of the recovery process. The same applies to WhatsApp or Telegram messages. It must be shown from which database file (for example, msgstore.db, wal/shm), in which version, and with which decryption method the message was obtained. More detailed information on this topic can be found in the article on using WhatsApp messages as evidence.

How to prevent it: Next to each finding, it should be written where, with which tool, and with which parameters that finding was obtained. Raw outputs (logs, screenshots, hexdump excerpts) should be added as appendices to the report.

7. A Contradictory Report

If what is said in one section of the report does not match what is said in another section of the same file, the report contradicts itself. For example, when the text section says "this IP address was identified" but the appendix table section lists a different IP, the report loses its integrity.

In the Court of Cassation's reversal grounds, it is frequently emphasized that a report cannot serve as the basis for a verdict because it contains internal inconsistency or because two reports issued by the same expert on different dates contradict each other. A contradictory report makes the judge hesitate and pushes the judge toward requesting a supplementary report or appointing a new expert.

How to prevent it: Before delivery, the report should be subjected to quality control by an independent second expert; numerical values, dates, file paths, hash values, and summary findings should be compared across sections.

8. Exceeding the Scope of Duty (Answering What Was Not Asked)

The questions the court poses to the expert in the appointment decision are limited. The expert's task is solely to give a technical answer to those questions. Making assessments of one's own accord on matters the judge did not ask about is considered exceeding the scope of duty.

The Court of Cassation's recurring approach is that an expert expressing an opinion on matters the court did not ask about undermines the report's admissibility. The judge reads the questions the report answers; the appended "additional assessments" carry no evidentiary value and may even cast a shadow over the report as a whole.

How to prevent it: The report should be structured by taking the questions in the appointment decision one by one, writing the answer to each question opposite it; additional matters should appear, if at all, only with a note that they are "left to the discretion of the court," in a separate section from the asked questions, and in a limited way.

9. Definitive Conclusions on Insufficient Evidence

In digital forensics, the results "could not be determined," "data could not be recovered," and "no log exists" are legitimate and valid results. The real problem is the expert leaping to a definitive conclusion on the basis of insufficient data. Declaring the absence of data is a professional stance; filling the absence of data with assumption is a methodological error.

A pattern that stands out in Court of Cassation rulings is that the available digital data (for example, evidence consisting of only a screenshot, a message printout presented solely on the user's statement, or an email whose original was not submitted) is presented in the report as a definitive finding without being put through a reliability test, which weakens the report's evidentiary value. In particular, the possibility that screenshot evidence has been manipulated is always on the agenda. Unless its source is verified, a screenshot of a mobile application interface is not, on its own, sufficient proof that the message was actually sent.

There is a similar problem with email evidence. A printout the user obtains from their own mail client does not provide assurance that the email actually came from that address, because the text can be edited on the client side. Valid email evidence must include the provider's server metadata (received headers, the DKIM signature, the SPF record). Definitive findings made on the basis of email without this metadata lead to the report's rejection.

How to prevent it: The expert should clearly state the adequacy of the data; where it is deficient, the limitation should be written as "a definitive determination could not be made on the basis of the available data; the original source (for example, a server log, a physical image of the phone, the email provider's metadata record) is required." If additional evidence needs to be requested from the court, one section of the report should explain this deficiency with its technical reasoning.

10. The Absence of a Digital or Electronic Signature

Under Law No. 5070, the Electronic Signature Law, the legal validity of documents produced in a digital environment is reinforced by a qualified electronic signature. Expert reports are now submitted electronically through UYAP in many courts, and this submission is made with the expert's qualified electronic signature.

A report that is unsigned or whose signature verification fails offers no assurance that its author is genuinely that expert. In Court of Cassation rulings, patterns have been documented in which the absence of a signature is treated as a ground for rejection on its own, or the report is turned away on the basis of a formal deficiency.

How to prevent it: Every report should be signed with the expert's qualified electronic signature; in physical delivery, a wet signature and seal should be present; and where necessary, a timestamp (TSA) should be added.

Supplementary Reports and Re-Examination Within the Framework of HMK Article 281

When a judge finds a report insufficient, the judge does not automatically reject it; first, within the framework of HMK Article 281, the judge collects the objections, identifies the points seen as deficient or contradictory, and requests a supplementary report from the same expert. This is a natural part of the report process.

A request for a supplementary report does not mean the expert did not do the job adequately; it is sometimes requested in order to assess the objections raised by the parties. However, when the supplementary report also falls short, or when the expert fails to resolve the contradictions in the root report while writing the supplementary one, the judge either appoints a new expert or does not base the verdict on the report. At this point, the procedure advances in this order: the root report, the parties' objections, the supplementary report, if necessary the report of a new expert panel, and at the final stage the judge's assessment.

The parties have the right to object after they learn of the report. Objections should be concrete, technical, and reasoned. Saying "the report is insufficient" is not enough; a technical justification should be provided, such as "the hash value was computed with MD5 instead of SHA-256, and the integrity guarantee is weak because of the possibility of collision." Concrete objections of this kind are the strongest support for the judge's decision to request a supplementary report.

An important point in the supplementary report process is the requirement that the expert not give an answer that contradicts the findings of their previous report. If what is said in the root report and what is said in the supplementary report are inconsistent with each other, the expert's technical credibility is damaged. In such cases, the judge most often appoints a new expert panel; this path is called a "three-member panel" or "expert panel" and generally involves bringing together experts from more than one discipline.

Expert Opinions in the Context of CMK Articles 67 and 73

In criminal proceedings, alongside the court-appointed expert, the parties may submit their own expert opinion on their behalf within the framework of CMK Articles 67/6 and 178. This opinion sets out, in technical language, the methodological errors, methodological deficiencies, or interpretive deviations seen in the appointed expert's report. An expert opinion is less a "counter-report" than a technical audit of the appointed report; it provides a concrete, reasoned, standards-based assessment of the report's admissibility.

When there is a contradiction between the court-appointed expert's report and the independent expert's opinion, the judge evaluates both documents; where necessary, the judge brings both experts together for a "joint examination." An expert opinion is one of the most powerful technical tools that can be used to obtain a report's rejection. CMK Article 178, while regulating the defendant's right to request that a witness or expert be heard for the collection of evidence, states that the court's ability to reject this request is subject to strict conditions.

In civil proceedings, under HMK Article 293, the parties may obtain an "expert opinion" and submit it to the file. This opinion is a separate evidentiary instrument from the report of the expert appointed by the court and is freely assessed by the judge. An expert opinion is used to give concrete shape to the objections to be raised against the appointed expert.

In areas such as digital evidence in divorce cases and spyware analysis, where the appointed expert cannot capture the broad scope, exposing the methodological gaps through an expert opinion is a common and effective approach. Particularly in mobile device examinations, cloud-based evidence analysis, and the detection of covert monitoring software (stalkerware), the details that an appointed expert with a narrow field of expertise overlooks are brought to light through an independent expert opinion.

Seven Practical Recommendations So That an Expert Report Is Not Rejected

The recommendations below serve as guidance both for colleagues working as experts and for parties whose files contain an expert report.

First, transparency of methodology is fundamental. In the first section of the report, the "hardware used, software, version number, method, and order" should be clearly written. ISO/IEC 27037, ISO/IEC 27042, and NIST SP 800-86 should be taken as references and, where necessary, added to the report as citations.

Second, the hash chain must be uninterrupted. The SHA-256 value of every file should be recorded and verified from imaging through the examination stage and on to report delivery. The fact that the same value can be reproduced over and over is the assurance.

Third, the raw data should be preserved as an appendix to the report. The expert should keep not only the result but also the raw output that leads to it (for example, log files, hexdump excerpts, message database tables, Cellebrite UFDR outputs) and be able to present it to the court when needed.

Fourth, one should not step outside the definition of duty. The questions in the appointment decision should be answered one by one, and one should stay away from legal interpretation, the characterization of a crime, and the areas that fall within the judge's discretion.

Fifth, missing data should be clearly stated. Saying "a definitive determination could not be made on this matter" is a professional stance; giving a definitive conclusion on an assumption corrupts the report. DSET's anti-hallucination approach rests on this principle: there is no unsourced claim, and every finding has its proof.

Sixth, the language of the report should be plain, academic, and dispassionate. Side expressions that favor one of the parties, such as "malicious" or "deliberately," should be avoided; the technical finding should be conveyed objectively.

Seventh, the report should be put through a review by a second expert before delivery. A report written alone may contain overlooked contradictions. An independent reading keeps the report standing throughout the court process.

Practices Derived From DSET's Case Experience

DSET is built on the field experience that founding expert HAMZA AYTAC DOGANAY gained over six years at the Cybercrime Unit of the General Directorate of Security and on the academic accumulation of a thesis-based master's degree in Digital Forensics from Ankara University. This background has provided the opportunity to observe firsthand both how digital evidence is collected during the investigation phase and how a report is tested during the court process.

The practices derived from this case experience converge on the following points:

A report's survival in court begins not at the moment the report is written, but at the moment the digital material is seized. If the report is deficient at the very first moment, no subsequent technical excellence can close that gap.

A common mistake is keeping the methodology section short under the pressure of delivering the report in haste. One of the most frequently encountered patterns in the Court of Cassation's reversals is reports in which the conclusion is written out in detail but the method is glossed over. The method is the backbone of the report.

Another practical observation is the expert exceeding the scope of duty in examinations that involve a KVKK violation. In material containing personal data, including side content not specified in the appointment decision in the report is both contrary to procedure and creates risk in terms of KVKK. The principle that the report remains limited solely to the scope of the appointment decision should be applied scrupulously.

In mobile device examinations, particularly during the extraction of data from end-to-end encrypted applications such as WhatsApp and Signal, having the technical details of the method used appear in full in the report ensures that the report withstands technical audit. The versions of tools such as Cellebrite UFED, Oxygen Forensic Detective, or Magnet AXIOM and which extraction profile was used (logical, file system, full file system, physical) should be clearly stated.

Timestamp consistency should be ensured between the crime scene reports and the technical findings in the report. Failure to correctly record the UTC offset, the local time, and the system clock can make the report appear contradictory.

In the context of digital forensics services in Ankara, DSET applies the ten rejection categories above as a checklist both in court-appointed expert reports and in expert opinions requested by the parties. Before the report is delivered, verification is performed on a category-by-category basis, and the points where deficiencies are identified are closed with additional evidence or additional methodology.

The Judge's Process of Evaluating the Report

When the judge takes up the report, the judge first asks these questions: Does this report answer the questions in the appointment decision? Is the method clear? Is it reproducible? Are there contradictions? Has it strayed into legal interpretation? Is the hash chain complete? Are the signature and formal requirements in order?

If the answer to any of these questions is "no," the judge, also taking into account the parties' objections, chooses one of the paths of requesting a supplementary report, appointing a new expert, or not basing the verdict on the report. The Court of Cassation's review proceeds along the same questions. In its reversal ruling, the Court of Cassation most often uses grounds such as "the method used in the expert report is insufficient," "the report is not of an auditable nature," or "the report contains a legal assessment that exceeds the scope of duty."

For this reason, the expert's task is not only to "find the correct answer" but to prove that the correct answer was reached "through a transparent method." There is an unspoken truth in digital forensics: no matter how correct the conclusion is, if the method is undefined the report is rejected; and even if the conclusion is limited, if the method is transparent the report stands.

The judge may not understand the technical part of the report; this is not the judge's fault but the nature of the field. The expert's task is to write the report "in a way the judge can understand." Excessive technical jargon, unexplained abbreviations, and unjustified technical assumptions render the report unusable for the judge. A good digital forensics report preserves its technical depth while also presenting a summary section for the judge to read. This summary is written in short, simple sentences; the technical details go in the appendix.

Conclusion: For the Report to Survive in Court

A digital forensics expert report is not merely a technical document; it is at the same time a legal argument. What convinces the judge is not the expert saying "my finding is correct," but the expert showing how the finding was made, with transparency, auditability, and methodological consistency.

The reversal rulings that can be reviewed in the Court of Cassation's public Case Search system display, again and again, ten basic rejection patterns: a broken chain of custody, missing hash, failure to use a write blocker, undefined methodology, drifting into legal interpretation, unsourced findings, internal contradiction, exceeding the scope of duty, definitive conclusions on insufficient data, and the absence of a digital signature. These patterns are the error map for the expert writing the report.

For an expert report to survive in court, the seven practical recommendations (transparency of methodology, the hash chain, preservation of raw data, the limit of the duty definition, declaration of missing data, plain language, and a second-expert review) must be applied as a whole. The supplementary report process within the framework of HMK Article 281 and the expert opinion mechanism within the framework of CMK Articles 67 and 178 are the legal instruments for testing the quality of a report.

DSET serves in Ankara and across Turkey both as a court-appointed expert and as an independent technical consultant providing expert opinions to the parties. It applies all the methodological steps required so that a digital forensics report is not rejected, in accordance with the ISO/IEC 27037, NIST SP 800-86, and SWGDE guidelines.

Every stage of the report process is built upon the one before it. If the crime scene report is deficient, the imaging step begins with a gap. If there is no image hash, the examination stage proceeds without a foundation. If the examination method is undefined, the conclusion is left hanging. Each link in this chain affects the report's admissibility in court. The most important lesson from DSET's case experience is this: the correct collection and correct reporting of digital evidence is not a one-time task but a series of standardized steps. The small inconsistencies introduced at each step ultimately put the entire report at risk.

The Court of Cassation's threshold of scrutiny has risen in recent years with the spread of digital evidence. Reports of the "it was examined and this conclusion was found" type, which were once considered adequate, are no longer accepted as sufficient today. A standards-based, sourced, traceable report that cites its basis stands up under the scrutiny of both the judge and the Court of Cassation. As this threshold rises, the competence level of digital forensics expertise must rise as well.

To Work With DSET

You can receive support from the DSET team on matters such as preparing a digital forensics expert report, submitting an expert opinion against an existing expert report, conducting a pre-trial methodological examination of digital evidence, or preparing a supplementary report under HMK Article 281.

Address: Hacettepe Teknokent, Ankara Phone: +90 536 662 38 09 Web: dset.com.tr

The expert opinion service covers testing the expert report in your case against the ten rejection categories listed above, setting out the deficiencies in technical language, and preparing the concrete justification needed to have the report referred for re-examination. To ensure the digital evidence in your case survives in court, putting your report through a methodological audit is the most critical step in the process.

Our process begins, in the first meeting, with a review of the expert report and its appendices in the case file. Next, the digital evidence sources (image copies, hash lists, and law enforcement reports, if any) are requested. When the technical analysis is complete, the methodological gaps the report carries, the points at which it falls into the Court of Cassation's reversal patterns, and the concrete objections that can be presented to the judge are gathered into an expert opinion document. This opinion is submitted to the file as evidence and, where necessary, forms the basis for an expert to be heard at the hearing.

By getting in touch, you can make an appointment for a preliminary review of the expert report in your case file. In the initial assessment phase, whether the report carries risk in terms of the ten rejection categories listed in this article is determined with a short checklist. Long years of field and academic experience provide you with a concrete road map for your report's survival in court.