Evidence Against My Company Was Obtained Illegally in Japan: Will it Be Excluded in Court?

The way evidence is collected by law enforcement is a cornerstone of a fair criminal justice system. If police investigators in Japan obtain evidence through illegal means, a critical question arises: can this evidence still be used against an individual or a company in court? This issue pertains to what is known as the "exclusionary rule for illegally obtained evidence" (ihō shūshū shōko haijo hōsoku, 違法収集証拠排除法則). Unlike some jurisdictions with broad, constitutionally mandated exclusionary rules, Japan's approach is more nuanced and has evolved through judicial precedent.

This article examines the principles governing the admissibility of illegally obtained evidence in Japanese criminal proceedings, including the landmark Supreme Court rulings that have shaped this area of law, and how illegality in prior investigative procedures can affect subsequently obtained evidence.

The Development of Japan's Exclusionary Rule

Historically, Japanese courts were often hesitant to exclude reliable physical evidence solely because of procedural illegalities in its collection. The primary focus was on the inherent probative value of the evidence itself – the idea being that a tangible piece of evidence doesn't change its nature simply because of how it was found. The Japanese Code of Criminal Procedure (CCP) does contain specific rules regarding the inadmissibility of involuntary confessions (CCP Article 319(1)), but it lacks a general, overarching statutory exclusionary rule for all types of illegally obtained physical evidence.

However, over time, judicial thinking evolved, driven by concerns that admitting all illegally obtained evidence would fail to deter unlawful investigative practices and could compromise the integrity of the judicial process. This led to the gradual adoption by the Supreme Court of what is often termed a "relative exclusion" approach (相対的排除説, sōtaiteki haijo-setsu). This approach does not mandate the automatic exclusion of evidence for any procedural error; rather, exclusion is reserved for situations where the illegality is deemed sufficiently severe.

The Landmark 1978 Supreme Court Decision: Establishing the Test

The foundational precedent for the modern exclusionary rule concerning physical evidence in Japan is the Supreme Court Decision of September 7, 1978 (Saikō Saibansho Kettei, Shōwa 53.9.7), Keishū Vol. 32, No. 6, p. 1672. This case involved stimulant drugs found during an illegal search of a suspect's inner jacket pocket conducted as part of a street questioning (an "inspection of belongings" that exceeded permissible limits).

The Supreme Court, while finding the search itself illegal, articulated a crucial two-pronged test to determine whether illegally obtained physical evidence should be excluded from trial:

1. Grave Illegality Nullifying the Spirit of the Warrant System (令状主義の精神を没却するような重大な違法, reijō shugi no seishin o bokkyaku suru yōna jūdai na ihō): The procedure used to obtain the evidence must involve a "grave illegality that nullifies (or fundamentally disregards) the spirit of the warrant system". This warrant system is prescribed by Article 35 of the Constitution (requiring warrants for searches and seizures) and further detailed in the CCP (e.g., Article 218(1)).
2. Unsuitability of Admission for Deterring Future Illegal Investigations (将来における違法な捜査の抑制の見地からして相当でない, shōrai ni okeru ihō na sōsa no yokusei no kenchi kara shite sōtō de nai): Admitting the evidence must be deemed "inappropriate from the standpoint of deterring future illegal investigations". This prong focuses on the prophylactic purpose of the exclusionary rule – to discourage unlawful police conduct.

In the 1978 case itself, despite finding the search of the pocket illegal, the Supreme Court did not exclude the drugs. The Court reasoned that the illegality was a "slight overstepping" of permissible bounds during what was otherwise a necessary and urgent street questioning. It noted there was no evidence that the officer intended to deliberately flout warrant requirements, nor was there any additional coercion used. Therefore, the Court concluded that the illegality was not "grave" enough to satisfy the first prong of the test, and admitting the evidence was not considered inappropriate from a deterrence perspective in those specific circumstances.

Factors Influencing "Grave Illegality" and "Deterrence"

While the 1978 Supreme Court test provides the framework, applying it involves considering several underlying factors that emerge from this and subsequent case law. Legal commentary (drawing from Prof. Asayama, as noted in the source material ) suggests these include:

• Degree of Deviation from Legal Norms: How significantly did the investigators depart from prescribed legal procedures? Was it a minor, technical error, or a fundamental violation of an individual's rights or established legal processes?
• Investigator's Intent (特に令状主義を潜脱する意図の有無, toku ni reijō shugi o sentatsu suru ito no umu – particularly the presence or absence of intent to evade the warrant system): Did the investigators act in bad faith? Did they intentionally or knowingly violate the law, especially with an aim to circumvent warrant requirements or other due process safeguards? Evidence of such intent weighs heavily in favor of exclusion.
• Presence and Degree of Coercion or Nature of Rights Infringement: Was physical force, psychological coercion, deception, or other improper pressure used in obtaining the evidence? How substantially were the individual's fundamental rights (e.g., privacy, bodily integrity, property rights) infringed by the illegal procedure?

For example, in the Tokyo District Court decision of November 25, 1987 (Shōwa 62.11.25), police officers possessed a search warrant for a suspect's home related to drug offenses, but this warrant did not authorize the seizure of urine. Officers told the suspect, "A warrant is out, so you have to provide a urine sample." The suspect, misunderstanding that this referred to a (non-existent) warrant for urine seizure, complied. The court found this to be a deceptive tactic that exploited the authority of the premises warrant to obtain the urine sample. This was deemed a grave violation of the warrant system with an intent to evade proper procedure, and the urine sample was excluded.

Exclusion Due to Illegality in Prior Procedures: The "Fruit of the Poisonous Tree"

Often, the evidence itself is obtained through a technically lawful procedure (e.g., a suspect "voluntarily" provides a sample, or evidence is found during a search under a subsequently issued warrant), but a prior investigative step was illegal (e.g., an unlawful arrest, an illegal "voluntary" accompaniment that amounted to a de facto arrest, or an earlier illegal search). This raises the question of whether the illegality of the earlier procedure taints the subsequently obtained evidence, a concept analogous to the "fruit of the poisonous tree" doctrine in U.S. law.

The Supreme Court Decision of April 25, 1986 (Saikō Saibansho Hanketsu, Shōwa 61.4.25), Keishū Vol. 40, No. 3, p. 215, was a key case addressing this. Police officers had entered a suspect's home without clear consent (the suspect initially thought they were debt collectors) and then "voluntarily" accompanied him to the police station. At the station, after some delay where his request to leave for an exam was not addressed, he provided a urine sample. The Supreme Court acknowledged that the legality of the urine sample collection needed to be assessed by considering the legality of the preceding accompaniment and detention at the station. The Court stated that a connection exists if:

1. The prior (illegal) procedure and the subsequent evidence-gathering procedure were aimed at the same investigative purpose.
2. The subsequent evidence gathering was a direct exploitation or utilization of the situation created by the prior illegality.

If such a close causal link is established, the illegality of the prior procedure can indeed taint the subsequently obtained evidence. The court then applies the same two-pronged test from the 1978 Supreme Court decision (grave illegality and deterrence) to determine if the now-tainted evidence should be excluded. In the 1986 case itself, while finding some illegal aspects in the initial entry and accompaniment, the Court ultimately found these were not "grave" enough to warrant exclusion of the urine sample, given that no physical force was used for accompaniment, the suspect did not resist once he realized they were police, and the urine sample itself was provided without overt coercion.

The Critical Role of Police Misconduct and Attenuation: The 2003 Supreme Court Case

The Supreme Court Decision of February 14, 2003 (Saikō Saibansho Hanketsu, Heisei 15.2.14), Keishū Vol. 57, No. 2, p. 121, provides a crucial illustration of both the exclusionary rule in action due to grave police misconduct and the concept of "attenuation" where the link between an initial illegality and later-obtained evidence can be broken.

• Facts: Police officers arrested a suspect for theft based on an arrest warrant. However, they failed to present the warrant to him at the scene of arrest or follow the procedures for emergency execution of a warrant (if they didn't have it physically with them). To compound this initial procedural violation, the officers later falsified official reports and provided false testimony in court to cover up their failure to properly execute the warrant procedure. Following this illegal arrest procedure, a urine sample was taken from the suspect at the police station, which tested positive for stimulant drugs. This positive test result then formed part of the basis for obtaining a search warrant for the suspect's home for drug-related evidence. During the execution of this drug search warrant (which was also conducted simultaneously with a pre-existing, valid search warrant for the home related to the original theft case), stimulant drugs were found and seized.
• Ruling on the Urine Sample: The Supreme Court found the initial arrest procedure to be gravely illegal. This was not just due to the failure to properly present the warrant, but significantly because of the subsequent police misconduct in falsifying reports and committing perjury to conceal their error. The Court deemed this conduct a "grave nullification of the spirit of the warrant system." The urine sample, taken on the same day and thus "closely related" to this gravely illegal arrest, was excluded from evidence. Admitting it, the Court reasoned, would not serve the purpose of deterring future illegal investigations.
• Ruling on the Drugs Seized from the Home: Despite the urine sample (which partly supported the drug search warrant) being excluded, the drugs seized from the suspect's home were admitted into evidence. The Supreme Court reasoned that the connection between the initial illegal arrest and the seizure of drugs from the home was not sufficiently "close" or direct. Several factors led to this conclusion of "attenuation":
  • The drugs were seized pursuant to a search warrant that had been reviewed and issued by a judge (even if one of its bases was now tainted).
  • Crucially, the search of the home was also being conducted under a separate, pre-existing, and entirely valid search warrant related to the original theft investigation. The police had lawful authority to be searching the premises for theft evidence regardless of the drug suspicions. It was plausible that the drugs could have been discovered during this lawful theft-related search (e.g., if found in plain view or in a location pertinent to the theft search).
  • This effectively broke the direct causal chain from the initial arrest illegality to the discovery of the drugs at the home. The taint of the illegal arrest did not extend fatally to this particular piece of evidence because of the intervening judicial warrant and the concurrent lawful search authority.

This 2003 decision powerfully illustrates that while severe police misconduct can lead to evidence exclusion, the "fruit of the poisonous tree" doctrine in Japan considers the directness of the link and the presence of intervening lawful processes or independent sources that might "attenuate" the taint of an earlier illegality.

The Supreme Court decision on X-ray inspections (September 28, 2009) also touched on this. While the warrantless X-ray itself was deemed an illegal compulsory "verification," the drugs later seized from the package under a subsequently obtained search and seizure warrant were admitted. The Court noted, among other factors, that there was a practical necessity for the X-ray, the courier had consented (though not the sender/recipient), police had tried to limit the X-ray to suspicious packages (suggesting no broad intent to evade the warrant system entirely), and the eventual seizure was under a judicial warrant which likely had other supporting evidence besides just the X-ray results. The illegality of the initial X-ray was not deemed grave enough in its totality to require exclusion of the evidence found via the later, warranted physical search.

Conclusion: A Balancing Act with a High Threshold for Exclusion

The exclusionary rule for illegally obtained evidence in Japan is not an automatic one. It is a "relative exclusion" doctrine applied by the courts based on a careful balancing of factors. The threshold for exclusion is high, generally requiring a "grave illegality that nullifies the spirit of the warrant system" and a determination that admitting the evidence would be contrary to the goal of deterring future unlawful police conduct.

When the illegality lies in a procedure prior to the actual collection of the evidence in question, courts will examine the causal link between the initial illegality and the subsequent evidence gathering. A direct exploitation of a prior illegality is more likely to lead to exclusion. However, intervening factors, such as the issuance of a valid judicial warrant based on information independent of (or significantly attenuated from) the initial taint, or the existence of an independent lawful basis for the discovery of the evidence, can break the causal chain and allow for the evidence's admission.

For businesses and individuals, this means that while procedural errors by police do not guarantee evidence will be thrown out, significant and deliberate violations of fundamental rights and warrant principles, especially those involving bad faith or attempts to cover up misconduct, stand a much greater chance of triggering the exclusionary rule in Japanese courts.