HOW JUDGES ASSESS THE CREDIBILITY OF EVIDENCE:
PROCEDURAL LAW PERSPECTIVES AND EVIDENTIARY STRATEGIES
Authored by:
Juventhy M. Siahaan, S.H., M.H.
Managing Partner, JBD Law Firm
I. Introduction
Behind the seemingly simple term "assessment of evidence" lies a complex intellectual activity involving authenticity, consistency, relevance, and the interrelationship between evidence, which leaves vast room for judicial discretion. Understanding this process is operational knowledge that determines how advocates construct evidentiary strategies, prepare documents and witnesses, and expose the weaknesses of the opposing party's evidence. This article examines it in an integrated manner: the civil evidentiary system (HIR/RBg and its jurisprudence), the transformation of the criminal evidentiary system through Law No. 20 of 2025 concerning the Criminal Procedure Code (KUHAP) effective since January 2, 2026, and the distinct evidentiary dimensions of the Administrative Court (PTUN), including the uncertainties inherent in a newly effective regime.
II. Evidence in Civil Cases
A. Authentic Deeds: Strong, but Not Unchallengeable
Article 165 of the HIR grants perfect (volledig bewijs) and binding (bindend bewijs) evidentiary strength to authentic deeds, but two critical limitations make this strength far from absolute. The first limitation is the valsheidsprocedure: The Supreme Court (MA) in Decision No. 3101 K/Pdt/1987 established the principle that once an allegation of forgery is raised with a substantial basis, the evidentiary strength of the deed is suspended, and its entire contents, including the preparation procedure and the capacity of the official, are open to re-examination. This principle contains a direct strategic implication: identifying every irregularity in the process of creating the deed submitted by the opposing party is a preliminary step that must not be overlooked.
The second limitation, which occurs more frequently in practice: an authentic deed proves formal strength, what the parties stated before an official, but not the substantive truth of what was stated. The MA in Decision No. 1014 K/Pdt/2001 established the principle that a judge is not only authorized but obligated to assess the consistency of the deed's content with the entirety of the existing evidence; substantial inconsistency is a valid basis for reducing its actual weight even if the deed remains formally valid. A judge who relies on a deed mechanically without assessing its context fails to perform their function as they should.
B. Presumptions, Admissions, and the Decisoir Oath
Presumptions (Article 173 HIR) are the most frequently underestimated evidentiary tool and the one most dependent on discretion. The MA in Decision No. 2592 K/Pdt/2006 established the principle that a series of mutually reinforcing facts, even if each is insufficient individually, can collectively surpass the value of a single formal piece of evidence. An effective strategy: building indicatieve feiten (indicative facts) whose inferences point toward the maintained position, and actively demonstrating those inferences to the judge rather than allowing the judge to form their own inferences without guidance. Admissions (Article 174 HIR) possess perfect strength only if they are absolute (zuivere bekentenis); a judge must accept or reject them in their entirety, so questions that prompt answers mixed between admission and defense actually weaken the evidentiary value. The decisoir oath (Articles 156–158 HIR) is not an evidentiary tool that hierarchically defeats an authentic deed; it is a closing instrument relevant precisely when evidence is balanced or insufficient; the party proposing it essentially entrusts the fate of the case to the integrity of their opponent.
C. Burden of Proof and Information Asymmetry
Beyond the principle of actori incumbit probatio (Article 163 HIR), what is more strategically decisive is when the burden shifts: once a prima facie case is established, the burden shifts to the opposing party to rebut it, forcing the opponent to operate in a defensive position. In contexts of extreme information asymmetry, the MA in Decision No. 835 K/Pdt/2013, a medical negligence dispute where the patient's medical records were exclusively in the hands of the hospital, established the principle that the party exclusively possessing relevant documentation cannot hide behind actori incumbit probatio to avoid the obligation to explain their actions. Crucial note: the MA applies this principle as a consideration in assessing the completeness of evidence, not as a formal reversal of the burden, a nuance critical to ensuring the argument is not attacked as an oversimplification.
III. Evidence in Criminal Cases: Transformation of the New KUHAP
The enactment of Law No. 20 of 2025 concerning the KUHAP since January 2, 2026, represents a paradigmatic shift. Because jurisprudence under this regime is still very limited, this condition contains uncertainty as well as strategic opportunities for practitioners who understand the direction of the changes.
A. Open Evidentiary System: From Five to Eight Types of Evidence
Article 235 paragraph (1) of the new KUHAP establishes eight categories of evidence: witness testimony, expert testimony, letters/documents, defendant's testimony, physical evidence (barang bukti), electronic evidence, judicial observation, and anything that can be used for proof as long as it is obtained in a non-unlawful manner. Three most concrete practical implications: scientific forensic evidence stands independently without being forced into other categories; electronic evidence is an independent type of evidence (Article 235 in conjunction with 242); and judicial observation of the demeanor of the defendant, witnesses, and the condition of physical evidence at trial now has explicit normative legitimacy. The eighth residual category opens the system to new types of evidence that could not be anticipated when the new KUHAP was designed.
B. Exclusionary Rule as a Positive Legal Norm
The codification of the exclusionary rule in Article 235 paragraphs (3)–(5) is the most strategically significant change. Article 235 paragraph (3) requires that every piece of evidence must have its authenticity proven and be obtained in a non-unlawful manner, cumulative dual requirements: it is not enough for the acquisition to be legal if authenticity cannot be verified, and vice versa. Article 235 paragraph (4) grants the judge active authority to assess both. Article 235 paragraph (5) establishes the consequence: evidence that is not authentic and/or obtained unlawfully cannot be used. The question "how was this evidence obtained" is now as fundamental as "what is the content of this evidence." Effective exclusion arguments must prove that the violation is substantive rather than a minor technicality and clearly prejudices the defendant's rights; the public prosecutor must be prepared to prove procedural compliance or the de minimis nature of any violation that occurred.
C. Abolition of the Minimum of Two Pieces of Evidence
Article 183 of the old KUHAP, the minimum of two pieces of evidence as a requirement for conviction, was not adopted in the new KUHAP. This requirement remains applicable for the naming of suspects and detention, but is no longer an explicit condition for conviction. The new KUHAP maintains the principle of in dubio pro reo and judicial conviction as absolute requirements, standards that, in practice, are very difficult to meet with a single piece of evidence without corroboration from an independent source. In the absence of established jurisprudence, judges will give greater weight to systematic arguments and those that honestly acknowledge uncertainty while offering a reasoned framework for assessment.
D. Hybrid System, Opening and Closing Statements, and Limits on Witness Examination
Article 4 of the new KUHAP establishes a blend of an active judge with balanced opposing parties. The opening statement (Article 231) is not merely a summary; it is a cognitive map guiding the judge to understand the evidence to be presented; the closing statement is not merely a conclusion; it integrates all evidence into a convincing narrative while responding directly to the opposing party's evidence. Article 236 explicitly prohibits suggestive questions (leading questions) that contain the desired answer, irrelevant questions, and misleading questions through the presumption of unproven facts, limitations that reflect the strengthening of the adversarial dimension and whose violation can eliminate the credibility of legal counsel at an irrecoverable moment.
E. Judicial Pardon and the Special Path
Article 246 in conjunction with Article 1 point 19 introduces the judicial pardon: a judge may declare a defendant proven guilty but not impose a criminal penalty if the lightness of the act, the personal circumstances of the perpetrator, the circumstances at the time the offense was committed, or, most revolutionarily, circumstances occurring thereafter are considered. The last clause allows the judge to consider post-offense loss recovery, changes in the social conditions of the perpetrator, or an actual impact that is more minimal than originally alleged. The implications are twofold: defense strategy must build evidence on pardon factors even when the commission of the offense is difficult to refute; prosecution strategy must build a narrative of sustained and unrecovered impact to counter this mechanism. The special path (Article 78) allows for summary proceedings upon the defendant's confession, but the judge is obligated to reject it if the confession is not supported by or contradicts the existing evidence.
F. Chain of Custody as an Absolute Prerequisite
Physical evidence as independent evidence requires an unbroken chain of custody, from investigators to the laboratory, to the prosecutor, to the court, all documented. Every gap opens an opportunity for exclusion based on Article 235 paragraph (5). Systematic investigation includes: where the physical evidence was stored and who had access; whether there are signs of modification or damage; whether the reports of seizure, handover, and storage are complete and consistent with one another.
IV. Evidence in the Administrative Court (PTUN): Distinct Dimensions of Administrative Disputes
Law No. 5 of 1986 in conjunction with Law No. 51 of 2009 (PTUN Law) Articles 100–107 regulates a fundamentally different evidentiary system. Article 100 recognizes the judge's knowledge as a valid type of evidence, a category unknown in the HIR in the same sense. Article 107 grants the judge the authority to determine what must be proven, establish the burden of proof, and present additional evidence beyond what is submitted by the parties. The consequence: the party concealing relevant information risks facing a forced production order which is almost always more damaging than voluntary submission with an adequate explanation; conversely, a party actively identifying specific documents in the hands of an administrative body and requesting the judge to order their production can use the authority of Article 107 as a strategic instrument.
In the PTUN, there is an evidentiary dimension absent in civil or criminal cases: the credibility of the administrative body's decision-making process itself. PTUN judges assess not only substantive facts but also compliance with the General Principles of Good Administration (AAUPB - Law No. 30 of 2014). A violation of the audi alteram partem principle, that the affected party was not given an opportunity to be heard before the decision was rendered, holds very high evidentiary value even when substantive evidence appears more doubtful. Inconsistencies in the administrative body's internal documents, between initial findings and final conclusions, or between an examiner's recommendation and the authorized official's decision, can serve as strong evidence of a violation of the principle of sufficient motivation (Article 10 letter f of the AP Law) and the principle of legal certainty.
V. Five Cross-Regime Factors Shaping Judicial Assessment
First, consistency, both internal and between evidence: documents whose dates or contents are inconsistent with the overall chronology will immediately draw the judge's suspicion, even if they are formally authentic deeds; consistency is a prerequisite for credibility, not just a favorable factor. Second, timeliness: contemporaneous records receive significantly higher weight than documents created after a dispute has arisen. Third, the interest of the source: testimony from an interested party requires corroboration from an independent source. Fourth, the completeness of the narrative: gaps, missing documents, witnesses not presented, and unanswered questions will be filled by the judge with their own inferences; a party that does not close its narrative gaps surrenders that freedom to the judge. Fifth, most rarely acknowledged openly but most consistently considered by experienced practitioners, is the composition and background of the panel of judges: judges with a commercial civil background tend to give greater weight to contractual documentation; judges with experience in economic crimes are more sensitive to transaction patterns and digital footprints. Searching previous decisions of the panel examining the case is a strategic step that must not be ignored.
VI. Witness and Expert Testimony
Judges evaluate testimony through three dimensions beyond its content: consistency with physical and documentary evidence, a witness whose testimony contradicts contemporaneous documents loses significant credibility regardless of the delivery; the manner of responding to pressure, a witness who becomes defensive or substantively changes testimony when pressed sends signals noted by the judge; and the balance of specificity, details that are too perfect for events from years ago actually raise suspicion that the testimony has been memorized, while a reasonable uncertainty over things that are indeed impossible to remember actually enhances credibility. Expert testimony that acknowledges the limitations and uncertainties of its conclusions is paradoxically more credible, as it shows that scientific truth is prioritized over the interests of the party presenting them.
VII. Electronic Evidence
For criminal cases, Article 242 of the new KUHAP makes electronic evidence an independent type of evidence; for civil cases, Articles 5–6 of the UU ITE require the use of electronic systems in accordance with regulations, a requirement not regulated in the HIR which becomes the most frequent loophole used to attack electronic evidence in civil cases. Authenticity is the central challenge in both regimes: Article 235 paragraph (3) of the new KUHAP makes the burden of authentication normative, such that presenting a digital forensic expert cannot be sidelined. Metadata, when a file was created and when it was last modified, is determinative: inconsistencies in metadata with the date listed on the document represent a serious authentication issue. Messages extracted from a longer conversation without the preceding and succeeding context can have a very different meaning; presenting the broader context is a step that must not be ignored.
VIII. Five Most Frequent Evidentiary Errors
The first error is submitting evidence without a narrative that integrates it into the overall argument. Judges do not always understand the relevance of a document unless it is explicitly explained and linked to the argument being proven; documents submitted without context risk being ignored or assessed much lower than intended. The submission of evidence must always be accompanied by an explanation positioning it within the overall narrative.
The second error is relying on volume as a substitute for quality. Submitting dozens of documents burdens the judge, obscures truly strong evidence, and gives the opposing party many loopholes to attack. It is more effective to focus the argument on four or five of the strongest pieces of evidence with perfect authenticity and context, rather than submitting twenty pieces of evidence where half are vulnerable to attack.
The third error, whose consequences are most serious under the new KUHAP, is failing to investigate the opposing party's method of obtaining evidence. With the exclusionary rule as a positive legal norm, failing to identify weaknesses in the chain of custody or acquisition procedures is an abandonment of the strongest weapon now available. Every search, wiretap, and investigative examination must have its procedures systematically traced before trial.
The fourth error is inconsistent testimony between examination sessions, more often born from sessions attended by different people without adequate briefing on what was stated previously, rather than from bad faith. A skilled examiner stores and compares all statements from various sessions; even minor inconsistencies will be used to question the credibility of the entire testimony. The solution: strict documentation of the substance of every session and thorough briefing before the next session for everyone who will provide testimony.
The fifth error is ignoring the entire new evidentiary dimensions opened by the new KUHAP. Judicial pardon, the exclusionary rule, and the open system each open evidentiary spaces that did not exist before: the party prosecuting does not prepare arguments against potential exclusion; the party defending does not build evidence for judicial pardon factors even when the commission of the offense is difficult to refute. This is a typical error of a transitional period whose consequences become increasingly costly as jurisprudence under this new regime grows.
IX. Closing
The assessment of evidentiary credibility by a judge is a process far more complex, more nuanced, and more dependent on discretion than appears from the surface of procedural law regulations. The new KUHAP adds a transformative layer through an open evidentiary system, the codification of the exclusionary rule, the strengthening of the adversarial dimension, and the judicial pardon with its revolutionary "circumstances occurring thereafter" clause. On the civil side, the MA jurisprudence provides nuances not visible from the text of the HIR which is over a century old, including principles of the burden of proof in the context of information asymmetry and the mechanism of the decisoir oath working in conditions of balanced evidence. In the PTUN, the active authority of the judge based on Article 107 of the PTUN Law and the evidentiary dimension of the administrative body's decision-making process add layers unknown in the other two systems.
Four strategic implications apply across regimes. First, proof begins long before trial: contemporaneous evidence radiates a credibility that cannot be matched by documents created later. Second, an effective strategy builds a consistent narrative from various mutually reinforcing independent sources and considers the background and record of the panel of judges examining the case. Third, weakening the opposing party's evidence is as important as building one's own: internal inconsistencies, chain of custody issues, procedural violations, and non-compliance with electronic system requirements are points of attack that must be identified and presented systematically. Fourth, the uncertainty of jurisprudence in the transitional era of the new KUHAP actually amplifies the value of deep legal expertise: the party that first succeeds in fighting for interpretations of key provisions will shape the direction of Indonesian criminal procedure for the next generation.