Investigator's Notes Under Scrutiny: The Disclosure of Interrogation Memos in Japanese Criminal Cases

During the intense process of criminal interrogation, investigators often jot down notes, create memos, or maintain logs to aid their memory, structure their questioning, or prepare official statements (kyojutsu chōsho 供述調書). Historically, such internal notes were largely considered private work product, shielded from the eyes of the defense. However, a series of landmark decisions by the Supreme Court of Japan, coupled with evolving evidence disclosure rules, has significantly shifted this landscape. Now, these once-internal documents can find themselves under judicial scrutiny and may be subject to disclosure to the defense, particularly if they pertain to the circumstances or credibility of a suspect's or witness's statements. This article explores the legal framework and key judicial pronouncements governing the disclosure of investigators' interrogation memos and memoranda in Japanese criminal proceedings.

The Framework of Evidence Disclosure in Japan: A Shift Towards Transparency

Japan's criminal trial system operates on an adversarial model, where the prosecution and defense present their cases before a neutral court. While this model has long been in place, the rules and practices surrounding pre-trial evidence disclosure have undergone significant evolution.

Historically, defense access to the prosecution's evidence was somewhat limited, with courts often cautious about broad "fishing expedition" requests. A key Supreme Court decision on April 25, 1969 (Keishū Vol. 23, No. 4, p. 248), established that courts could order disclosure of specific prosecution-held evidence only if the defense demonstrated a concrete necessity, the evidence was particularly important for their preparation, and there was no overriding risk of negative consequences such as evidence tampering or witness intimidation.

However, to enhance the efficiency and focus of trials, especially with the introduction of the lay judge system (saiban-in seido 裁判員制度), Japan undertook substantial reforms of its Code of Criminal Procedure (CCP), which came into effect in November 2005. These reforms aimed to clarify and expand evidence disclosure obligations, particularly through a structured pre-trial conference procedure (kōhan-zen seiri tetsuzuki 公判前整理手続). This procedure mandates various stages of disclosure:

1. Prosecutor's Initial Disclosure (CCP Art. 316-14): When a case is designated for a pre-trial conference, the prosecutor must first submit a document outlining the "facts intended to be proved" (shōmei yotei jijitsu 証明予定事実). Following this, they must disclose to the defense the evidence they plan to use to prove these facts. This includes allowing inspection and copying of documentary and physical evidence, and providing details of witnesses they intend to call, along with relevant portions of any prior statements made by those witnesses.
2. Defense-Requested Disclosure of Specific Categories of Evidence (Ruikei Shōko Kaiji - CCP Art. 316-15): After the initial prosecutorial disclosure, the defense can request access to certain defined categories of evidence held by the prosecution that are deemed important for assessing the credibility of the evidence already disclosed by the prosecutor. This includes prior statements of prosecution witnesses, the defendant's own statements, and other relevant materials.
3. Defense-Requested Disclosure of Claim-Related Evidence (Shuchō Kanren Shōko Kaiji - CCP Art. 316-20): Once the defense has outlined its own factual and legal arguments in response to the prosecution's case, they can request disclosure of any further evidence held by the prosecution that is relevant to these specific defense claims or points of dispute.

In both category-based and claim-related disclosure requests, the prosecutor is obliged to disclose if it is deemed "appropriate," considering the necessity for defense preparation against the potential risks of harm or abuse arising from disclosure. If disputes arise, the court has the authority to issue a binding ruling ordering disclosure if it finds that the prosecution has improperly withheld discoverable evidence (CCP Art. 316-26).

Are Investigators' Memos and Notes "Evidence" Subject to Disclosure?

The question of whether an investigator's handwritten notes, internal memos, or personal logs taken during or concerning an interrogation fall within these disclosure obligations has been a significant point of legal contention.

A crucial regulation often cited in this context is Article 13 of the Criminal Investigation Norms (犯罪捜査規範 - Hanzai Sōsa Kihan), a set of national police regulations. It stipulates: "Police officers, when conducting investigations, must, in consideration of appearing as a witness in the public trial of the case and to contribute to future investigations, meticulously record the progress and other matters that should serve as reference." This rule suggests an expectation that such records are created as part of official duties and maintained.

Landmark Supreme Court Decisions on the Disclosure of Investigator Notes

Several pivotal decisions by the Supreme Court of Japan have clarified the status of these internal investigative notes, generally expanding the scope of what may be discoverable by the defense.

A. The Supreme Court Decision of December 25, 2007 (Keishū Vol. 61, No. 9, p. 895):
This case set a foundational precedent. The defense, challenging the voluntariness of a suspect's confession, sought disclosure of the interrogating police officer's handwritten memos.

• The initial District Court had rejected the request, viewing such memos as personal notes created for the investigator's own use in preparing formal statements, and thus inherently not subject to disclosure.
• The Tokyo High Court, however, overturned this. It reasoned that even if such notes were not directly in the prosecutor's physical possession, if the prosecutor could easily obtain them from the police, they were difficult for the defense to access independently, and were highly relevant to the defense's arguments regarding the interrogation, they should be considered "evidence the prosecutor should retain" and thus subject to disclosure. The High Court also noted that Criminal Investigation Norms Article 13 implied such records should exist.
• The Supreme Court largely affirmed the High Court's stance, but with important distinctions:
  • It held that evidence subject to a disclosure order is not strictly limited to items currently in the prosecutor's files. It can extend to documents created or obtained during the investigation, currently held by a public official in their official capacity, and easily obtainable by the prosecutor.
  • Crucially, the Court distinguished between purely personal jottings made solely for an investigator's private use (which would not be disclosable) and more formal records.
  • It found that memoranda (bibōroku 備忘録) created by a police officer pursuant to their duties under Criminal Investigation Norms Article 13, which record the progress of an interrogation or other matters for reference and are retained by the investigative agency, transcend the status of "personal memos." Such documents are considered "official documents related to the investigation" (sōsa kankei no kōbunsho 捜査関係の公文書). As such, they can be subject to a disclosure order if they are relevant to issues being litigated at trial, such as the circumstances surrounding an interrogation or the voluntariness of a confession.

B. The Supreme Court Decision of June 25, 2008 (Keishū Vol. 62, No. 6, p. 1886):
This decision reaffirmed the principles laid out in the December 2007 ruling. Significantly, it also established that the court itself has the authority to order the prosecutor to present such contested memos to the court for an in-camera inspection. This allows the judge to privately review the notes to determine if they meet the criteria for disclosure to the defense, balancing the defense's need for information against any legitimate concerns about revealing sensitive investigative strategies or unrelated information.

C. The Supreme Court Decision of September 30, 2008 (Keishū Vol. 62, No. 8, p. 2753 - Notes in a Privately Purchased Notebook):
This case further refined the concept of "official" notes.

• Facts: An investigating police officer had used a notebook he purchased with his own money to take notes during various investigations, including the interrogation of a key witness (Witness A). Witness A later provided new, crucial testimony to the prosecutor that was not in his earlier formal police statement (which had been drafted by Officer B using these notebook entries to refresh his memory). The defense sought disclosure of Officer B's notebook entries concerning the earlier interrogation of Witness A to assess the consistency and credibility of Witness A's evolving account. Officer B had kept the notebook in his desk at work, took it home upon transfer, and brought it to his new station when the prosecutor made inquiries related to the case.
• Supreme Court's Ruling: The Supreme Court affirmed the lower courts' orders for disclosure. It reasoned that even though the notebook was privately purchased, the notes within it were created by Officer B in his capacity as a police officer, during the execution of his official duties, and for official purposes. Therefore, the notes possessed a "public nature" (kōteki na seishitsu 公的な性質) and were considered to be "officially retained" (shokumu-jō hokan 職務上保管), even if physically kept in a personal item or temporarily taken home. Since the notes were easily obtainable by the prosecutor and were relevant to the critical issue of Witness A's credibility and the consistency of his statements, disclosure was deemed necessary for the defense.
  (It's worth noting a dissenting opinion from Justice Kainaka in this case, who argued that the defense had not sufficiently made Officer B's initial interrogation of Witness A a direct point of contention that would necessitate revealing B's personal notes, especially since Witness A's formal police statement had already been disclosed. The dissent suggested that the proper way to explore statement consistency would have been to examine Officer B as a witness first.)

Implications and Scope of Disclosure

These Supreme Court decisions have had a significant impact, effectively broadening the potential scope of evidence disclosure to include many types of investigators' notes that might previously have been considered purely internal or personal.

• The "Official Duty" Nexus: The determining factor is generally whether the notes were created in the course of, and for the purpose of, official duties. The physical medium (e.g., an official-issue notebook versus a privately purchased one) is less important than the context and purpose of their creation and retention.
• Criminal Investigation Norms Article 13: This regulation acts as a strong underpinning for the argument that such note-taking is an official duty, making the resulting records presumptively official in nature.

However, disclosure is not automatic or unlimited:

• Truly Personal Jottings: Notes that are purely subjective reflections, personal reminders unrelated to specific investigative actions or deponent statements, or thoughts not intended to form any part of an official record, may still be protected from disclosure.
• Relevance and Necessity: The standard tests for evidence disclosure still apply. The defense must demonstrate that the notes are relevant to their specific claims or to assessing the credibility of prosecution evidence, and that disclosure is necessary for preparing their defense.
• Example of Non-Disclosure (N-System Data): Courts have generally held that raw data from widespread surveillance systems like automatic license plate readers (N-System), if considered general police intelligence not specifically created or compiled for the investigation of the particular case at hand, is not subject to disclosure. However, analysis reports derived from such data specifically for the case might be disclosable if the defense can establish their relevance and necessity (though in cited examples, such requests were often denied on these grounds).

Practical Considerations for Investigators

The clear implication of these judicial pronouncements is that investigators in Japan should operate under the assumption that almost any note or memo created in an official capacity concerning an investigation could potentially be subject to disclosure and judicial review. This encourages:

• Maintaining notes in a professional, objective, and accurate manner.
• Understanding that using personal notebooks for official investigative jottings does not automatically shield those contents from disclosure if they otherwise meet the criteria of being official records.
• Being prepared to explain the context and purpose of any notes taken.

Conclusion

Japanese law, as interpreted by its Supreme Court, has moved towards greater transparency regarding the materials that may underlie formal investigative records like interrogation statements. Investigators' contemporaneous notes, memos, and logs are no longer automatically considered off-limits to the defense. If these documents are deemed to be "official documents related to the investigation," created in the course of duty, and are shown to be relevant and necessary for the defense—particularly concerning the circumstances of an interrogation or the credibility of statements derived from it—courts have the authority to, and will, order their disclosure. This development reflects an ongoing effort to balance the needs of effective investigation with the defendant's right to a fair trial and access to information pertinent to their defense, while still attempting to draw a line between official records and purely private, non-evidentiary jottings.