Was the Street Stop and Search of Your Bag Lawful? Exclusion of Illegally Obtained Evidence in Japanese Drug Cases

You were stopped on the street, asked to show what was in your bag, and arrested when drugs were found. Or officers were waiting outside your home, or your car was pulled over. People who have been caught in this way often ask us whether the police were allowed to do that. How an investigation began is not merely background. It feeds directly into a legal question: whether what was found may be used as evidence. This article avoids passing judgment on the lawfulness of any particular case and sets out, in general terms, the perspectives from which such questions are examined.

Key points

• In drug cases the seized item is usually the decisive evidence, so the way it was obtained can become a live issue.
• Street questioning is an administrative activity under the Police Duties Execution Act and may not extend to compulsion.
• The limits of a search of belongings have been discussed in terms of consent, the manner of the search, and its necessity and proportionality.
• Whether evidence should be excluded where there was illegality is assessed by asking how serious the illegality was and whether exclusion is appropriate.
• Memories of how it all began fade quickly, so recording the sequence of events as early as possible is valuable.

Why does it matter how a drug investigation began?

In drug cases, the item seized or the sample taken is in practice the central evidence. How that item came into the hands of the investigating authorities therefore bears directly on whether it is admissible. As a general proposition, the Supreme Court of Japan has established a framework under which evidence may be excluded where there was serious illegality in the way it was obtained and where admitting it would not be appropriate.

In practice, such arguments succeed only in limited circumstances, and it is not our intention to encourage unrealistic hopes. Even so, unless the records are obtained and the sequence of events is reconstructed in detail, the question never arises for consideration at all. For defence counsel, that reconstruction is where the work starts.

Can you refuse a police street stop in Japan?

Street questioning is carried out under the Police Duties Execution Act, which allows officers to question a person where there are reasonable grounds to suspect that the person has committed an offence, among other situations. The basic understanding is that it is a voluntary activity, and that it may not extend to compulsion that overrides the will of the person questioned.

On the street, however, the line between voluntary and compulsory is not always clear. If you were kept in place for a long time, or surrounded by several officers so that leaving was not realistically possible, or if your car keys were taken from you, whether the encounter stayed within voluntary limits becomes a proper subject of examination. The assessment turns on the specific circumstances taken as a whole: what led to the questioning, what the suspicion rested on, how long you were held there, and what was said during that time.

What are the limits on a search of your belongings?

A search of belongings is likewise premised on consent. Where a person has not agreed and officers nonetheless take items out of a bag or put a hand into a pocket, the question arises whether what occurred amounted in substance to a search. If conduct equivalent to a search was carried out without a warrant, the issue becomes whether the warrant requirement was circumvented.

In examining this, the following are checked one by one. How each of them is assessed varies enormously from case to case, so please read them as a framework for examination rather than as a rule of thumb.

• Whether consent was actually requested in words before the search began
• If consent is said to have been given, whether its meaning was conveyed accurately in your own language
• Whether physical force was used, and to what degree
• The time of day, the location, and the number of officers present
• What is later given in the record as the basis for the suspicion

When the reason for approaching a foreign national is itself in question

Foreign nationals sometimes tell us they cannot understand why they, and no one else, were stopped. What prompted the approach is connected to whether grounds for suspicion existed, and as a general matter it deserves examination.

This is an area that has also been the subject of public debate. We do not prejudge any individual case. What we do is check what reasons appear in the record and test whether they are consistent with the objective circumstances at the time. Recalling the scene may be unpleasant, but hearing concretely about the time, the place, who else was around and what words were exchanged is where that verification starts.

How does challenging the start of the investigation connect to your right to stay in Japan?

In drug cases involving foreign nationals, examining how the evidence was gathered forms the core of the first line of defence. Article 24, item 4, sub-item (chi) of the Immigration Control and Refugee Recognition Act (入管法24条4号チ) makes a person who has been convicted of violating the Narcotics and Psychotropics Control Act, the Act on Regulation of Cannabis Plant Cultivation, the Opium Act, the Stimulants Control Act, the Anti-Drug Special Provisions Act, or Chapter XIV of Part II of the Penal Code subject to deportation (退去強制). It places no limit on the type of sentence or its length. A fine, and a suspended sentence, fall equally within it.

Given that structure, obtaining a suspended sentence at trial is not the finishing line when measured against your status of residence (在留資格). Our office designs the defence in three stages: a decision not to prosecute (不起訴処分) before charges are filed as the first line, contesting the deportation proceedings as the second, and special permission to stay (在留特別許可) as the third. Where doubts remain about how the evidence was collected, raising that clearly at an early stage both strengthens the first line and leaves a record that can be referred to in the later stages.

About our office

At Funado International Law Office, attorney Daisuke Matsumura personally handles every stage, from the first visit at the detention facility through to the close of trial. Recollection of the moment of arrest fades day by day, so we place weight on visiting as early as possible and hearing what happened in detail.

For Chinese we have a dedicated interpreter on staff who is experienced in cases involving foreign nationals. Separate from the interpreter appointed by the investigating authorities, this interpreter works for the client and is available throughout the criminal process, which makes it possible to go over delicate points such as whether consent was given and what exactly was said, in the client's own language. For languages other than Chinese, we arrange an interpreter according to the needs of the case. For residence procedures after the criminal case ends, we work together with an affiliated administrative scrivener.

From the cases we have handled

In one matter, a client prosecuted under the Stimulants Control Act for possession with profit-making purpose (営利目的) was acquitted after thorough analysis of the evidence and sustained examination of the defendant and cross-examination of witnesses. Where the heart of a case lies in how the evidence is assessed, the patient work of testing each item in the record decides the outcome.

In another matter, a woman in her twenties accused of withdrawing money as part of an organised fraud scheme obtained a decision not to prosecute after we argued the subjective circumstances as a whole. We also have experience in international criminal cases, cases tried before lay judges, and serious cases reported worldwide.

When something about the start of an investigation troubles you and you say nothing, the record will show that nothing happened. Whether to challenge it is a judgment to be made after reading the file, but the first step is to preserve the facts accurately. Write down what you can remember of the arrest and speak with a lawyer early. Please note that this article is a general explanation; for your own case, consult a lawyer directly. Past results reflect the particular circumstances of those cases and are not a guarantee of a similar outcome.

This article reflects the law as at August 2026.

About the author

Daisuke Matsumura, Attorney at Law
Dai-Ichi Tokyo Bar Association (registration no. 59077, admitted 2019)
Funado International Law Office (Fuse Building Main Wing 3F, 3-4-10 Takada, Toshima-ku, Tokyo)
Practice focused on criminal defence for foreign nationals and immigration proceedings.
Results include an acquittal in a Stimulants Control Act case (possession for the purpose of profit), non-prosecution in organised fraud cases, and special permission to stay in cases regarded as difficult.

Funado International Law Office
Website: https://matsumura-lawoffice.jp/
WeChat ID: matsumura1119