Expert reports in criminal cases can be decisive in Turkey because many criminal files turn on questions a judge cannot answer with ordinary legal knowledge alone. Technical causation, medical findings, digital traces, accounting flows, signature analysis, valuation issues, and scientific measurements often enter the case through an expert report rather than through a witness or a simple document. Yet Turkish criminal procedure does not treat expert evidence as untouchable. On the contrary, it builds a structured system around when an expert may be appointed, what an expert may and may not say, how the report must be served on the parties, how objections may be raised, when a supplementary or new report may be sought, when the expert can be examined in court, and how the court must explain its reliance on expert material in the final judgment. Expert evidence in Turkey is therefore powerful, but never above challenge.
The constitutional foundation matters from the start. Article 36 of the Constitution protects the right to a fair trial through legitimate means and procedures. Article 38 protects the presumption of innocence and states that findings obtained through unlawful methods cannot be treated as evidence. Turkish criminal procedure then translates those principles into trial rules that require the court to decide the case only on lawfully obtained evidence discussed in the hearing, to reject unlawfully obtained evidence when its production is requested, and to explain in the reasoning of a conviction which evidence was accepted and rejected, including material obtained by unlawful methods. This constitutional and procedural structure is important because an expert report is only one item of evidence within a larger lawful-proof system. It is not a substitute for judicial reasoning, and it does not relieve the court of its duty to decide law and fact properly.
The first core rule appears in Article 63 of the Code of Criminal Procedure. Expert opinion may be obtained where resolving an issue requires expertise or special or technical knowledge, either ex officio or on the request of the prosecutor, the injured party, the suspect, the accused, counsel, or the legal representative. But the same article draws a strict limit: an expert cannot be heard on matters that can be resolved through the general and legal knowledge required of a judge. That line is one of the most important challenge points in practice. If the report is being used not to explain a technical issue but to tell the court how to apply the law, how to characterize the offense, or how to weigh evidence in a judicial sense, then the expert has crossed into a zone reserved to the court. Under Turkish law, that is not a small drafting mistake. It goes to the proper role of the expert in the case.
That same limit is reinforced by the broader expert-witness framework in the Bilirkişilik Kanunu. Article 3 of that law states that the expert must act independently, impartially, and objectively; may not make statements outside matters requiring expertise or technical knowledge; may not make legal qualification or legal evaluation; may not be appointed where the issue can be solved through general knowledge or the legal knowledge required of a judge; must perform the task personally; and may not be assigned unless the technical issue and the scope and limits of the examination are clearly identified. The same article also states that, as a rule, one report should be taken on the same matter, although a supplementary report may be requested to cure a deficiency or ambiguity. These are not abstract policy statements. They are practical standards against which criminal expert reports can and should be measured. (Bilirkişilik Daire Başkanlığı)
A lawful appointment order must also be specific. Article 66 of the Code requires the appointment decision to state the technical questions to be answered, the subject of the examination, and the time limit for performance. The ordinary period may not exceed three months, though it may be extended once for up to three more months if special reasons require it and the appointing authority gives a reasoned decision. If the expert does not submit the report within the allotted time, the expert may be replaced immediately; the expert must then submit a report explaining what has been done so far and return the materials received, and may also face removal from the roster and liability for damage caused by delay. These provisions matter because a defense challenge is stronger when it can show not only that the report is weak, but that the expert’s mandate itself was vague, overbroad, or not followed.
Turkish law also regulates how the expert may conduct the work. Article 66 states that the expert performs the task in communication with the appointing authority, may provide updates, and may ask that useful measures be taken. The expert may seek information from persons other than the suspect or accused in order to carry out the task. If clarification is needed on a subject outside the expert’s own field, the judge, court, or prosecutor may permit the expert to consult qualified persons known for their knowledge, and the reports they provide are added to the file as a supplementary part of the expert report. The parties may also request that specifically identified persons who can provide technical information be heard during the examination or that particular research steps be taken. This is highly relevant for objections: where an expert relied on outside input, the defense should check whether the Code’s consultation route was followed and whether the resulting material was actually placed in the file.
The report itself is governed mainly by Article 67. When the examination ends, the expert must submit a signed report describing the work carried out and the conclusions reached. If more than one expert is appointed and they disagree, the differing views or any separate views on common conclusions must be stated together with reasons. Article 67 then repeats a crucial substantive limit: the expert report may not contain legal evaluations that belong to the judge. This is one of the most useful provisions for defense counsel. A report that strays from forensic analysis into statements such as “the accused committed fraud,” “the elements of the offense are present,” or “criminal intent is established” can be attacked as exceeding the lawful scope of expert evidence. The court may of course infer legal conclusions from technical facts, but the expert may not usurp that judicial function.
Service of the report is also a rights issue. Article 67 states that copies of the report are served on the prosecutor, the participant, the suspect or accused, defense counsel, or the legal representative, whether directly at the hearing or by registered delivery. Most importantly, once the expert examination is complete, the parties must be given time so that they can request a new expert examination or submit objections. If such requests are rejected, a reasoned decision must be given within three days. This is one of the clearest legal bases for challenging an expert report in a Turkish criminal file. The Code does not expect the defense to accept the report silently. It expressly expects a procedural window for objections and for requesting a new examination.
Article 67 also gives the parties a powerful additional tool: the prosecutor, the participant, the suspect or accused, defense counsel, or the legal representative may obtain a scientific opinion from their own expert concerning the event, for use in preparing the expert report, or on the report itself. This is the Turkish procedural basis for a private expert opinion, usually referred to in practice as an uzman mütalaası. The Code adds that no separate extension of time is granted merely because such an opinion is being obtained. The practical meaning is important. Turkish law affirmatively allows party-side expert rebuttal, but it expects counsel to use that mechanism promptly and strategically rather than assuming that the timetable of the case will automatically expand.
Once the case reaches trial, Article 68 becomes central. The court may at any time decide to hear the expert in the hearing, and it may also summon the expert for explanations on the request of one of the interested parties. The same rule applies to the expert who prepared the party’s scientific opinion. This is a major challenge mechanism. If the written report is incomplete, vague, internally inconsistent, methodologically thin, or overconfident, defense counsel should not stop at written objections. Turkish law expressly allows the court to hear both the court-appointed expert and, upon request, the expert who prepared the party’s own scientific opinion. In a criminal case, that hearing may be the only realistic opportunity to expose assumptions, missing data, methodological shortcuts, or confusion between technical opinion and legal conclusion.
The hearing stage also matters because Article 201 allows the public prosecutor and the lawyer participating as defense counsel or representative to put direct questions to experts, along with the accused, witnesses, and other persons called to the hearing, subject to courtroom discipline. That means Turkish criminal procedure does provide a genuine route for adversarial testing of expert evidence. When read together with Article 68, Article 201 makes clear that challenging an expert report is not confined to paperwork. The defense may seek live examination of the expert and put questions directly aimed at the reliability, scope, assumptions, data set, methods, omissions, and conclusions of the report.
A separate and very important challenge route concerns recusal. Article 69 states that the same grounds that justify the recusal of a judge also apply to an expert. The prosecutor, the participant, the suspect or accused, defense counsel, or the legal representative may exercise that right. The name of the court-appointed expert must be disclosed to the persons entitled to object, unless an impediment exists. The recusal request is decided by the judge or court handling the case; in the investigation phase, if the prosecutor does not accept the request, the criminal judgeship of peace decides. The person seeking recusal must explain the reason and the supporting facts. In practice, this means that where there is an appearance of bias, institutional conflict, prior involvement, or another disqualifying circumstance, the expert can be challenged directly rather than merely criticized on the merits.
The Bilirkişilik Kanunu strengthens the logic of such objections because it states at the level of basic principles that the expert must be independent, impartial, and objective, must perform the task personally, and must keep entrusted information confidential even after the assignment ends. The same framework is supported by the Bilirkişilik Yönetmeliği, which places experts in a system of regional boards, rosters, oversight, and performance tracking. The Ministry’s regulation also shows that the rosters record, among other things, how many supplementary reports were needed because the expert left questions unanswered or answered them incorrectly. That background matters because it demonstrates that Turkish law does not see expert performance as immune from institutional scrutiny. A defense challenge to an expert report is not contrary to the system; it is built into the way the system is supposed to function. (Bilirkişilik Daire Başkanlığı)
From a defense perspective, the first substantive challenge question should always be whether the issue was genuinely expert territory at all. Under Article 63 of the Code and Article 3 of the Bilirkişilik Kanunu, no expert should be appointed for matters the judge can decide using ordinary legal knowledge, common knowledge, or judicial assessment. This challenge matters especially in white-collar, tax, banking, cyber, or negligence cases, where expert reports sometimes slide from technical explanation into telling the court what result to reach. If the “expert” is effectively performing legal interpretation, credibility analysis, or ultimate guilt determination, the defense should object that the report exceeds the proper boundaries of expertise.
The second challenge question is whether the report stayed within the mandate. Article 66 requires that the order identify the questions to be answered, the subject of examination, and its scope. Article 3 of the Bilirkişilik Kanunu likewise forbids appointment unless the technical problem and the scope and limits of the review are clearly specified. So if the report answers questions that were never asked, ignores questions that were asked, relies on materials outside the order, or expands into areas not assigned, the defense has a strong statutory objection. In practice, overreach and underreach often occur together: the expert may intrude into law while failing to answer the actual technical issues posed by the court or prosecutor.
The third major challenge concerns methodology and reasoning. Article 67 requires the expert to explain the operations performed and the conclusions reached. That does not mean a bare conclusion is enough. A persuasive criminal-law objection will ask whether the report identifies the materials examined, the method used, the steps taken, the margin of uncertainty where relevant, the reasons for accepting one technical scenario over others, and the basis for each conclusion. Turkish law does not state this in the language of modern forensic-science treatises, but the combined effect of Article 67 and the duty of reasoned judgment in Article 230 is that opaque reports are vulnerable. A court cannot rationally explain why it relied on a report if the report itself does not explain how it got where it got.
The fourth challenge is internal inconsistency or disagreement between experts. Article 67 expressly states that, where multiple experts have differing opinions or separate views on common conclusions, those differences must be written into the report with reasons. That matters because a criminal court should not be allowed to flatten genuine scientific disagreement into a false appearance of unanimity. If the panel contains diverging views, or if one report conflicts with another report in the file, the defense should insist that the disagreement be addressed explicitly rather than brushed aside with a formula such as “the court found one report persuasive.” In criminal cases, unexamined inconsistency is often the strongest sign that the technical picture is not as certain as the accusation suggests.
The fifth challenge is lateness or incomplete performance. Article 66 gives the expert three months as the ordinary deadline, extendable once for up to three more months with a reasoned decision, and authorizes immediate replacement if the expert does not report on time. It also requires the late expert to explain what has been done and return the materials received. This matters because delay is not a neutral inconvenience in criminal cases. It may prolong detention, delay trial, prevent timely objections, or impair the defense’s ability to gather rebuttal evidence. If the expert exceeds the statutory period without a proper extension, or if the report is filed in a way that undermines defense rights, replacement and renewed examination become entirely legitimate requests under the Code.
The sixth challenge concerns unlawful foundations. If the expert report relies on evidence obtained unlawfully, the report may become vulnerable together with its underlying material. Article 206 requires the court to reject evidence that was obtained unlawfully. Article 217 states that the offense may be proved only with lawfully obtained evidence. Article 230 requires the court to show separately and expressly any evidence in the file obtained through unlawful methods. And Article 289 treats it as a form of absolute unlawfulness if the judgment relies on evidence obtained unlawfully, if the reasoning required by Article 230 is missing, or if the right of defense was restricted on a matter important to the judgment. For expert reports, this means the defense should always ask not only whether the report is analytically sound, but also whether the samples, digital images, documents, measurements, or other source materials on which it rests entered the file lawfully.
A related practical issue is how far the court is bound by the expert report. Turkish criminal procedure does not make the expert the decision-maker. Article 217 gives the court free judicial evaluation of the evidence presented and discussed in the hearing, subject to legality. Article 230 then requires the judgment to discuss and assess the evidence and to state which evidence was accepted and rejected. The result is that the court may rely on an expert report, but it must explain why. It cannot lawfully outsource the verdict to the expert, and it cannot avoid dealing with defense objections by saying, in effect, “the expert has spoken.” A report may be persuasive, but the judicial duty of evaluation remains with the court.
This point becomes especially important when the defense has sought a supplementary report or a new expert examination and the request has been denied. Article 67 requires a reasoned decision within three days if such a request is rejected. That means the refusal itself can later become part of the appellate record. If the court or prosecutor rejects a new examination even though the report is incomplete, contradictory, exceeds technical bounds, or ignores material objections, the defense should preserve that issue carefully. The appeal or cassation argument is not only that the report was weak; it is that the procedural right to a meaningful challenge under Article 67 was cut off without legally adequate reasoning.
There is also a practical route that is often underused. Article 178, reflected in the official Ministry text, states that if the court rejects the request by the accused or the participant to summon a witness or expert, the accused or participant may bring that person directly to the hearing, and the person is then heard. Combined with Article 68, this means that even when the court is reluctant to call an expert important to the defense, Turkish procedure still gives the defense a route to put live expert evidence before the trial court. In an expert-heavy criminal case, that can be the difference between a written objection that remains abstract and a live technical confrontation that forces the weaknesses of the prosecution report into the open.
In conclusion, expert reports in criminal cases are central in Turkey, but they are never beyond challenge. The Code of Criminal Procedure limits expert use to genuinely technical matters, requires a defined mandate and timeline, forbids legal evaluation by the expert, gives the parties time to object and seek a new examination, authorizes private scientific opinions, allows live examination of both court-appointed and private experts, permits recusal on grounds analogous to judicial recusal, and requires the court to base the judgment only on lawfully obtained evidence discussed in the hearing. The wider Bilirkişilik regime reinforces independence, impartiality, objectivity, personal performance, clear scope definition, and the principle that one report is normally enough unless supplementation is needed to cure deficiencies. For defense lawyers, the practical lesson is simple: do not treat an expert report as a conclusion. Treat it as evidence with rules, limits, and vulnerabilities. In Turkish criminal litigation, a well-targeted challenge to an expert report can reshape the entire case.
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