Evidence Law in Criminal Proceedings

Evidence Law in Criminal Proceedings. The primary objective of criminal procedure is to ascertain the “material truth” concerning an alleged crime. This is an indispensable goal for the realization of justice and the preservation of social order. However, the modern rule of law does not accept achieving this goal at any cost. The process of seeking the material truth must be conducted in observance of the fundamental rights and freedoms of the suspect or accused, as guaranteed by the Constitution and international conventions, particularly the “right to a fair trial.” It is at this juncture that the rules of evidence in criminal procedure emerge as the most fundamental mechanism for striking the delicate balance between the obligation to seek the material truth and the necessity of protecting individual rights. While evidence serves as a source of light illuminating the crime, the manner in which it is obtained and evaluated constitutes the cornerstone of a fair trial.

The central issue this article will address is how the principle of “free evaluation of evidence,” adopted by the Turkish criminal procedure system, is constrained by “evidence prohibitions,” and how the interaction between these two opposing poles is reflected in judicial decisions. On one hand, there is the judge’s authority to freely evaluate any lawful evidence according to their conscientious conviction; on the other, there is the absolute obligation to exclude findings obtained through unlawful means, regardless of their significance. The dialectical relationship between these two fundamental principles determines the fairness and legitimacy of the criminal justice system.

In this comprehensive review, the fundamental concepts of evidence theory and the main principles governing criminal procedure (the system of conscientious conviction, the principle of immediacy of evidence, the principle of in dubio pro reo) will first be analyzed in depth. Subsequently, the procedural journey of evidence, from its collection in the investigation phase to its discussion before the court in the prosecution phase, will be examined. One of the most critical sections of the article will be the constitutional and legal foundations of the prohibition on evaluating unlawfully obtained evidence and the concrete reflections of the “fruit of the poisonous tree” doctrine, an extension of this prohibition, in the case law of the Court of Cassation. Finally, special types of evidence such as witness testimony, expert reports, and expert opinions will be examined in detail in terms of their probative value and reliability. This analysis aims to reveal how theory is put into practice by focusing not only on positive law but also on the current and guiding decisions of the Court of Cassation.

Part 1: The Foundations of Evidence Theory in Criminal Procedure

The theoretical framework shaping the evidence regime in the Turkish criminal procedure system is built upon fundamental principles that interact with and balance each other. Understanding these principles is essential for grasping the logic of the entire process, from the collection of evidence to its use as a basis for a verdict.

1.1. The Concept, Qualities, and Function of Evidence

Definition and Function

In criminal procedure law, evidence, in its most general sense, is any means used to prove an event (the crime) alleged to have occurred in the past. More technically, evidence refers to “all information and material that proves the commission of the crime” and “the tools and methods used by judicial authorities to investigate whether a crime was committed and by whom.” Evidence serves two fundamental and interconnected functions in the criminal procedure process:

To Establish the Occurrence of the Event: Evidence is used to prove whether the material elements of the alleged crime (the act, the perpetrator, the victim, the causal link, etc.) have occurred.
To Form the Judge’s Conscientious Conviction: Evidence helps the judge, who will render the verdict at the end of the trial, to reach a conviction free from doubt about how the event transpired.

These two functions form the basis of the principle “no conviction without evidence” and ensure that a just decision can only be based on concrete proof.

Qualities of Evidence

For a finding or piece of information to be accepted as “evidence” in criminal procedure and to be used as a basis for a verdict, it must possess certain qualities. These qualities are the fundamental criteria that determine the probative value and reliability of the evidence:

Realism: The evidence must reflect real events and not be based on assumptions or fictions. It must be consistent with the nature of things and the ordinary course of life.
Rationality: The evidence must be based on a logical foundation and not contradict the rules of reasoning. Elements that are contrary to logic or based on superstitions do not qualify as evidence.
Accessibility: The evidence must be accessible, examinable, and debatable by the court and the parties. Information that exists only in one person’s mind and cannot be presented concretely cannot be considered evidence.
Representativeness of the Event: The evidence must have a direct or indirect connection to the event under trial and serve to clarify the dispute. A finding unrelated to the event has no evidentiary value.
Commonality: The evidence must have been presented to all parties in the proceedings (the prosecution, the defense, the court) and opened for discussion. Evidence that one of the parties is unaware of or has not had the opportunity to discuss cannot be used as a basis for a verdict. This is a requirement of the adversarial principle.
Legality: This is the most fundamental and indispensable quality of evidence. The evidence must be obtained in accordance with the procedures prescribed in the Constitution and laws. Findings obtained through unlawful means cannot be accepted as evidence, even if they possess all other qualities.

1.2. Main Principles Governing the Evaluation of Evidence

1.2.1. The System of Conscientious Conviction and the Principle of Free Evaluation of Evidence

Although rigid and formal systems like the “legal evidence system” were applied in the evaluation of evidence in the past, modern criminal procedure law has adopted the “system of conscientious conviction.” The Turkish legal system is also based on this system. At the core of this system lies the judge’s ability to reach a conviction by freely evaluating the evidence. The judge, with exceptions specified in the law, does not establish a hierarchy among the evidence; for example, they may give more weight to a witness’s testimony than to a documentary evidence, or vice versa. What is important is that the judge evaluates all lawfully submitted evidence as a whole, through a logical filter, and justifies the conclusion reached.

However, this freedom does not imply unlimited arbitrariness. The judge’s discretion is limited by various mechanisms. Firstly, the judge is bound by the Constitution and laws. Their evaluation must be impartial, objective, and logical. Most importantly, the conscientious conviction reached by the judge cannot be an abstract belief or a personal intuition. According to Article 217, paragraph 1 of the Code of Criminal Procedure (CMK) No. 5271, the judge can base their decision “only on evidence that has been brought to the hearing and discussed in their presence.” Therefore, the conscientious conviction must be a rational and justified conclusion, subject to the scrutiny of the parties within the publicity and adversarial nature of the trial.

A dynamic tension exists between the “principle of free evaluation of evidence” and the principles of “legality” and “in dubio pro reo.” This serves as a “checks and balances” mechanism that prevents the system from sliding into arbitrariness. The broad discretion granted to the judge is first restricted by the rule that “unlawfully obtained evidence cannot be used.” The judge does not have the authority to “freely” evaluate unlawful evidence; they are obliged to disregard it completely. In the evaluation of the remaining lawful evidence, if this evidence does not establish guilt “beyond all doubt,” the “in dubio pro reo” principle comes into play. This principle compels the judge to use their discretion in favor of acquittal. This sequence demonstrates that the judge’s “conscientious conviction” is not an abstract belief but a rational and justified conclusion that has passed through these legal and logical filters.

1.2.2. The Principle of Immediacy of Evidence (Vasıtasızlık)

This principle signifies that the court that will render the verdict must have direct contact with the evidence, without an intermediary (such as an investigation phase statement record). The logic behind the principle is the assumption that information is more reliable when obtained from its source. For example, a requirement of this principle is that a witness be heard in person before the court, rather than having their statement taken by law enforcement during the investigation phase read out at the hearing. This allows the judge to observe not only what the witness says but also how they say it, their demeanor, gestures, facial expressions, and any hesitation or confidence in their voice. These non-verbal cues can provide important clues about the credibility of the statement.

The principle of immediacy of evidence is fully applied primarily in the prosecution (trial) phase, which is the center of the proceedings. Since the purpose of the investigation phase is to collect evidence to determine whether there is sufficient suspicion to file a public lawsuit, the full application of the principle is not expected at this stage. In an era where digitalization and remote access technologies are increasingly integrated into the judiciary, this principle serves as a bulwark protecting the human dimension of the trial and the importance of the judge’s personal perception. Investigation files, written transcripts of witness statements, and expert reports are “indirect” representations of the event. The principle of “immediacy” compels the court not to be content with these representations but to resort to the “direct” sources of the event (the witness themselves, the scene of the event, the crime weapon, etc.). This direct contact allows the judge to test not only what is said but also the manner in which it is said, its consistency, and its credibility with their five senses. This increases the likelihood of reaching the material truth and strengthens the right to a fair trial, especially in cases where testimonial evidence is critical. Thus, the principle prevents the trial from being reduced to a mere file review.

1.2.3. The Principle of “In Dubio Pro Reo” (Benefit of the Doubt to the Accused)

As one of the most fundamental safeguards of criminal procedure and one of the most important reflections of the rule of law, the principle of “in dubio pro reo” is a natural consequence of the “presumption of innocence.” According to the presumption of innocence, guaranteed by Article 38 of the Constitution and Article 6 of the European Convention on Human Rights, a person is considered innocent until their guilt is proven by a final court decision. This principle means that the burden of proof lies with the prosecution (the Public Prosecutor), and the accused is not obliged to prove their innocence.

The “in dubio pro reo” principle comes into play when this burden of proof is not met. If, at the end of the trial, despite all the evidence collected, there remains a reasonable doubt in the court’s conscientious conviction as to whether the accused committed the crime, this doubt must be interpreted not against the accused, but in their favor. A criminal conviction must be based not on a high probability or a possible opinion, but on clear and certain proof, free from all doubt.

The scope of this principle is quite broad. It applies not only to doubts about whether the crime was committed but also to any unresolved doubts regarding material facts that affect the accused’s legal situation, such as the nature of the crime (e.g., whether the act was intentional injury or attempted murder), the manner of its commission (e.g., whether the threat was made with or without a weapon), and the existence of reasons that reduce or eliminate criminal responsibility. As this is a rule of proof (sübut), it primarily comes into play during the prosecution phase, at the moment the court is forming its judgment. It does not apply during the investigation phase, as the existence of “sufficient suspicion” is considered adequate to issue an indictment.

Part 2: The Journey of Evidence in Procedural Law: From Investigation to Prosecution

Evidence transforms from static findings into dynamic means of proof by passing through specific stages in the criminal procedure process. This process is primarily divided into the investigation and prosecution phases, each with its own rules and actors for collecting and evaluating evidence.

2.1. Evidence Collection in the Investigation Phase

The investigation phase begins when suspicion of a crime is learned and continues until the indictment is accepted. The main purpose of this phase is to investigate the material truth, collect evidence, and determine whether there is sufficient suspicion to file a lawsuit.

Authority and Responsibility

The authority and responsibility for collecting evidence in the investigation phase primarily belong to the Public Prosecutor. The prosecutor manages the investigation and usually carries out this duty through the judicial police officers (police, gendarmerie) under their command. The judicial police conduct crime scene investigations, take statements from witnesses and the suspect, and collect and preserve material evidence in accordance with the prosecutor’s instructions. The prosecutor may also perform these actions personally if deemed necessary.

The Obligation to Collect Evidence For and Against the Suspect (CMK Art. 160/2)

The role of the Public Prosecutor in the investigation extends beyond that of a one-sided accuser. Article 160, paragraph 2 of the CMK imposes a very important obligation on the prosecutor: The prosecutor is “obligated to collect and preserve evidence for and against the suspect through the judicial police officers under their command, and to protect the rights of the suspect, in order to investigate the material truth and ensure a fair trial.” This provision is the most concrete reflection of the principles of “equality of arms” and a fair trial in the investigation phase. The prosecutor’s duty of objectivity prevents them from focusing only on evidence that confirms suspicion; on the contrary, it requires them to investigate and add to the file any evidence that could demonstrate the suspect’s innocence or change the nature of the crime.

Although the prosecution phase is theoretically considered the center of the trial, in practice, the evidence collected (or neglected and not collected) during the investigation phase largely determines the fate of the case. A prosecutor’s failure to collect exculpatory evidence can lead to consequences that are very difficult or impossible to remedy in the prosecution phase. For example, although the prosecutor is obliged to collect exculpatory evidence under CMK Art. 160/2, the suspect and their lawyer may not have the opportunity to fully supervise how objectively this process is conducted due to the confidentiality of the investigation. If the prosecutor fails to collect recordings from a camera at the scene that could prove the suspect’s innocence, and these recordings are eventually deleted, this critical evidence will no longer be available during the prosecution phase. This strikingly illustrates the difficulty of translating the “equality of arms” principle from theory into practice and how vital the prosecutor’s objectivity is for a fair trial. A fair prosecution can only be built on a foundation of evidence that has been fairly and completely collected during the investigation.

Collectible Evidence

During the investigation phase, any type of evidence can be collected, provided it is lawful. This includes witness statements, suspect statements, victim statements, discovery and crime scene investigation reports, expert reports, material evidence obtained from searches and seizures, wiretap recordings, camera footage, and other documents. This evidence is added to the investigation file and forms the basis for the prosecutor’s decision on whether to file a lawsuit.

2.2. Presentation and Discussion of Evidence in the Prosecution Phase

The prosecution phase begins with the court’s acceptance of the indictment and continues until the judgment becomes final. The center of this phase is the trial, where evidence is presented and discussed.

The Centrality of the Trial

The trial is the heart of criminal procedure. Unlike the confidentiality of the investigation phase, the trial is generally public. At this stage, the principles of “orality,” “immediacy,” and “adversarial proceedings” are fully realized. Evidence collected during the investigation phase is presented for discussion by the parties at the trial by being read, heard, or examined. The judge can base their decision only on the evidence that has gone through this discussion process and has been brought to the trial (CMK Art. 217/1).

Introduction of Evidence and Cross-Examination

At the trial, the prosecution and defense present their evidence (introduction of evidence). The Public Prosecutor presents the evidence specified in the indictment, while the defendant and their counsel present evidence supporting their defense. Witnesses and experts are summoned to the trial and heard directly.

Cross-examination, one of the most effective ways to verify the accuracy and reliability of evidence, allows the parties (and the court) to directly question the opposing party’s witnesses, experts, or specialists. This mechanism is of critical importance for testing the credibility of testimonial evidence, revealing contradictions, and contributing to the clarification of the material truth. The parties attempt to expose the weak or inconsistent aspects of the statements through the questions they ask. This process enables the judge to evaluate the evidence more soundly.

Part 3: An Absolute Fortress: The Prohibition on the Evaluation of Unlawfully Obtained Evidence

The strictest, most uncompromising, and most fundamental rule of Turkish evidence law is that evidence obtained through unlawful means cannot be used in a trial. This prohibition is a manifestation of the rule of law, which dictates that the goal of reaching the material truth, no matter how important, cannot be achieved by violating the law and fundamental human rights.

3.1. Constitutional and Legal Basis of Evidence Prohibitions

The normative basis for evidence prohibitions is found in the Constitution, at the top of the hierarchy.

Constitutional Basis: Article 38, paragraph 6 of the Constitution of the Republic of Turkey states, with a clarity that leaves no room for interpretation, “Findings obtained contrary to law shall not be considered as evidence.” This provision establishes that evidence prohibitions are a constitutional guarantee and that even the legislator cannot circumvent this rule.
Legal Regulations: This fundamental constitutional principle is concretized in various articles of the Code of Criminal Procedure, providing procedural safeguards:
- CMK Art. 217/2: This article outlines the framework of proof, stating that “The imputed crime can be proven with any kind of evidence obtained in a lawful manner,” thereby setting “legality” as the ground of legitimacy for the act of proving.
- CMK Art. 206/2-a: This article regulates that during the presentation of evidence at the trial, the court will reject the evidence if “the evidence was obtained unlawfully.”
- CMK Art. 230/1-b: This article imposes an obligation on the court to explain in the reasoning of its judgment “the discussion and evaluation of the evidence, the evidence on which the judgment is based and the evidence that was rejected; and within this scope, to separately state and justify why any evidence in the file that was obtained through unlawful methods was not taken as a basis for the judgment.”
- CMK Art. 289/1-i: In the appellate review (temyiz), this article considers “the judgment being based on evidence obtained through unlawful methods” as an absolute reason for reversal (a case of absolute illegality). This means that a judgment based on unlawfully obtained evidence will be overturned without any further examination.
The Absolute Nature of the Prohibition: In the system adopted in Turkish law, the evidence prohibition is absolute. This means that unlawfully obtained evidence, no matter how clearly it proves the defendant’s guilt, can absolutely not be used in the trial and cannot be the basis for a judgment. As consistently emphasized in the jurisprudence of the Court of Cassation, it is irrelevant who created the unlawfulness of the evidence (a public official or a private person) or whether the unlawfulness in obtaining the evidence was intentional or negligent. The violation of the rule renders the evidence “poisonous” and necessitates its exclusion from the judicial system.

3.2. The “Fruit of the Poisonous Tree” Doctrine and Its Reflections in Turkish Law

Definition of the Doctrine

A logical extension of the prohibition on evaluating unlawfully obtained evidence is the doctrine known in the Anglo-Saxon legal system as the “Fruit of the Poisonous Tree.” In Continental European law, this is referred to as the “remote effect of unlawfully obtained evidence.” According to this doctrine, not only the evidence directly obtained through an unlawful method (the poisonous tree) but also all other evidence obtained by relying on or as a result of this unlawful evidence (the poisonous fruits) are considered unlawful and cannot be used in the trial. For example, crime instruments seized during a raid on an address learned through an illegal wiretap, even if the raid was based on a proper search warrant, are considered unlawful as they are the “fruit of the poisonous tree.” This is because the initial step that led to this evidence (the wiretap) was unlawful.

Analysis of the Court of Cassation’s Jurisprudence

Although there is no explicit provision in Turkish criminal procedure legislation regulating this doctrine, the Court of Cassation, especially in its recent decisions, has consistently and strictly adopted this doctrine based on the absolute prohibitions in Article 38 of the Constitution and Article 217 of the CMK. According to the Court of Cassation, once unlawfulness taints the evidence, it renders all consequences derived from it legally invalid.

One of the most current and clear examples of this approach is the decision of the 10th Criminal Chamber of the Court of Cassation dated 10.01.2024, with file number 2022/4525 E. and decision number 2024/268 K. In this decision, it was stated that the defendants’ identities were determined based on an unlawfully obtained video recording. The Court of Cassation ruled that because this initial step (identity determination) was unlawful, all other evidence obtained after this determination was also unlawful under the rule that “the fruit of the poisonous tree is also poisonous” and could not be used as a basis for the judgment. This decision shows that the Court of Cassation includes not only the direct consequences of unlawful evidence but also its indirect and remote effects within the scope of the prohibition and applies the doctrine without hesitation.

The strict application of the “fruit of the poisonous tree” doctrine by the Court of Cassation creates a strong deterrent effect that shapes the future conduct of law enforcement, going beyond merely invalidating evidence in a specific case. This demonstrates that evidence prohibitions serve not only to remedy a past illegality but also to prevent future illegalities. Suppose that in an investigation, law enforcement officers identify a suspect through an improper method. Even if a search of the suspect’s home is conducted with a proper warrant based on this unlawful starting point and incriminating evidence is found, the Court of Cassation holds that the initial illegality taints and invalidates all subsequent evidence. As a result, a case file full of material evidence may end in an acquittal. Such decisions send a clear message to law enforcement agencies: “No evidence you obtain by circumventing procedures and taking shortcuts will have any legal value, and all your efforts will be in vain.” This is a significant outcome that encourages law enforcement units to act lawfully from the very beginning of an investigation and demonstrates the indirect impact of judicial decisions on law enforcement training and operational standards.

Part 4: An In-Depth Look at Special Types of Evidence and Their Probative Value

In criminal trials, a wide variety of evidence types are used to reach the material truth. However, some types of evidence hold special importance due to their nature, the way they are obtained, and their reliability, and they play a key role in determining the course of cases. This section will examine frequently encountered and highly debated types of evidence, such as testimonial evidence, expert evidence, and expert opinions, in terms of their probative value.

4.1. Testimonial Evidence

Testimonial evidence originates from a human source and emerges when a person explains their observations, knowledge, or opinion. Witness, defendant, and victim statements are the most important elements of this category.

4.1.1. Witness Testimony

Witness testimony is one of the oldest and most common means of proof in criminal procedure. It is the act of a person who has witnessed a criminal event with their five senses conveying this observation and knowledge before the court. However, witness testimony, no matter how important, is also the most problematic and most debated type of evidence in terms of reliability. Many factors can weaken the evidentiary value of witness testimony, such as the fallibility of human memory, the possibility of misperceiving or misremembering events, the fading of memories over time, and the possibility of the witness intentionally giving a false statement.

For these reasons, the judge must be extremely careful when evaluating witness testimony. In accordance with the system of conscientious conviction adopted by the CMK, the judge freely evaluates witness testimony along with other evidence. In this evaluation, factors such as the internal consistency of the witness’s statements, their coherence with other evidence in the file (material evidence, other witness statements, the defendant’s statement, etc.), the conditions under which the witness perceived the event, and their personal credibility are taken into account. Theoretically, even a single witness statement that the judge finds credible can be sufficient for a conviction; however, in such a case, the judgment’s reasoning must provide a very solid and convincing explanation of why such high probative value was attributed to this statement, its relationship with other evidence, and how any potential doubts were overcome.

4.1.2. Victim and Defendant Statements

Victim Statement: As the direct subject of the crime, the victim is one of the most important sources of information about the event. The victim’s statement is of vital importance, especially in cases like sexual offenses, where there is often no witness or other evidence. However, the possibility that the victim’s statement may not always be objective, as they are a party to the case and have been affected by the event, should not be overlooked. Therefore, as stated in the jurisprudence of the Court of Cassation, the victim’s statement must also be evaluated meticulously like other evidence and, if possible, supported by corroborating evidence.
Defendant’s Statement (Confession): A confession, where the defendant admits to committing the crime they are accused of, is an important piece of evidence. However, in modern criminal law, a confession is not regarded as the “queen of evidence.” For a defendant’s confession to be the basis of a judgment, two fundamental conditions must be met: First, the confession must be based on the defendant’s free will. Confessions obtained through prohibited interrogation methods listed in Article 148 of the CMK, such as torture, ill-treatment, fatigue, deception, or promises, cannot be evaluated as evidence, even with the defendant’s consent. Second, the confession should not be considered sufficient for a conviction on its own and must be supported by other material evidence in the file. This is a safeguard against the possibility of a defendant taking responsibility for a crime they did not commit for various reasons (such as protecting someone else or being under duress).

4.2. Expert Evidence and Expert Opinion

In criminal trials, situations that require special or technical knowledge beyond the judge’s general and legal knowledge are frequently encountered. In such cases, the court seeks the assistance of an expert.

4.2.1. Expert Report (CMK Art. 63 et seq.)

Expert testimony is the process of seeking the opinion of a person or institution appointed by the court or prosecutor on a matter whose resolution requires expertise, special, or technical knowledge. For example, whether a signature is forged is examined by a graphologist, the cause of death is determined by a forensic medicine expert, and whether an accounting record is irregular is examined by a financial advisor.

The most important feature of an expert report is that it is not binding on the judge. An expert report is a “discretionary piece of evidence,” just like all other evidence. The judge freely evaluates the report along with the other evidence in the file. If the judge finds the report insufficient, contradictory, or erroneous, they can request an additional report, appoint a new expert, or, by clearly stating the reasons, make a decision completely contrary to the report. Furthermore, the expert’s task is to make a technical determination; making a legal assessment (for example, determining who is “primarily” or “secondarily” at fault in an incident) is exclusively within the judge’s authority, and the expert cannot enter this domain.

4.2.2. Expert Opinion (CMK Art. 67/6)

Article 67, paragraph 6 of the CMK grants the parties (the Public Prosecutor, the complainant, the suspect or defendant, and their representatives) the right to obtain a scientific and technical report (expert opinion) from an expert of their own choosing regarding the matter under trial. The parties usually resort to this option to object to the report prepared by the official expert appointed by the court, to point out missing or erroneous findings in the report, or to base their own claims and defenses on a technical foundation.

An expert opinion, just like an expert report, is a “discretionary piece of evidence.” In doctrine and the jurisprudence of the Court of Cassation, it is accepted that there is no hierarchy or difference in legal value and probative force between the report of the expert appointed by the court and the expert opinion obtained by the parties. The judge freely evaluates both reports. If there is a contradiction between the reports, the judge can resolve this contradiction by hearing the experts at the trial, asking them questions, subjecting them to cross-examination, or obtaining a report from a new panel of experts.

The institution of expert opinion, regulated in CMK Art. 67/6, has transformed the theoretical principle of “equality of arms” into a concrete right, especially in technical and complex matters. This institution serves as a critical mechanism that prevents the defense from being at a disadvantage against the state’s expert power (Forensic Medicine Institute, Criminal Police Laboratories, etc.). In the traditional system, the court would appoint an expert, and the parties would have to content themselves with objecting to this report, often without technical knowledge. This was an asymmetrical struggle. Expert opinion, however, balances this asymmetry by giving the defense the opportunity to find its own expert and submit a counter-report. This situation transforms the trial from being based on the “authoritative opinion of a single expert” to a platform for “dialogue or debate among experts.” The judge is no longer confined to a single technical opinion; by listening to conflicting views and cross-examining the experts, they have the opportunity to better understand the essence of the matter and make a more sound decision. This means deepening the right to a fair trial and increasing the probability of reaching the material truth.

Table 1: Comparative Analysis of Expert Report and Expert Opinion

Criterion	Expert Report (CMK Art. 63 et seq.)	Expert Opinion (CMK Art. 67/6)
Appointing Authority	Public Prosecutor in the investigation, Judge/Court in the prosecution	The parties (Prosecutor, Complainant, Suspect/Defendant and their representatives)
Legal Nature	Discretionary evidence	Discretionary evidence
Binding Effect	Not binding on the judge. Freely assessed.	Not binding on the judge. Freely assessed.
Objectivity	Expected to be impartial as appointed by the court.	May be perceived as subjective since chosen by the parties, but content and scientific consistency are essential.
Role in Proceedings	To enlighten the court on technical matters.	Generally, to form a counter-argument to an existing expert report, to technically support the parties’ claims.
Objection Procedure	The report can be objected to; an additional report or a new expert can be requested.	The other party can submit a counter expert opinion; the court can be asked to take action to resolve the contradiction.

The rules of evidence in criminal procedure constitute the most critical juncture in the application of abstract legal norms to concrete events. These rules are the product of a dialectical structure that, on the one hand, embodies the ideal of reaching the material truth to meet society’s expectation of justice, and on the other, the obligation to protect the fundamental rights and freedoms of the individual. While the Turkish legal system adopts flexible principles such as “conscientious conviction” and “free evaluation of evidence,” it aims to establish a fair and balanced structure by surrounding this freedom with fundamental safeguards such as “legality,” “immediacy of evidence,” and “in dubio pro reo.”

An examination of judicial precedents, especially the recent decisions of the Court of Cassation, reveals a strong will to maintain this balance. In particular, the absolute exclusion of unlawfully obtained evidence and the unhesitating application of the “fruit of the poisonous tree” doctrine as an extension of this prohibition are the most important indicators that the principle of the rule of law and the right to a fair trial are not just words but are being put into practice. These precedents not only resolve the cases before them but also set a standard of conduct for investigative authorities for the future, creating a preventive effect on the overall functioning of the system.

Ultimately, the conscientious conviction reached by the judge in a criminal trial is not an abstract feeling, a personal intuition, or an arbitrary discretion. This conviction must be a rational synthesis of evidence that is not unlawful, is reasonable and logical, and has been publicly and adversarially discussed at the trial, within the definite limits drawn by the law. The law of evidence is the most fundamental guarantee that prevents this rational synthesis from turning into arbitrariness and ensures the legitimacy and reliability of the criminal justice system.

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