Under a Multi-Agency Investigation System, Where Does the Fruit-of-the-Poisonous-Tree Line Fall Between Seizure for a Separate Offence, Requests for Supplemental Investigation, and the Exclusion of Illegally Obtained Evidence?

Question

Where, during supplemental investigation after a case has been referred to the prosecution, a confession or statement of a suspect or witness, or documents voluntarily produced, are newly obtained on the basis of material that the first investigative agency collected outside the scope of a warrant or of the results of an interrogation conducted in breach of due process, is that derivative evidence admissible?

In a multi-agency system of investigation and prosecution in particular, an issue may arise where an agency at a later stage attempts to launder a procedural violation committed by the agency at an earlier stage through formally lawful procedures (drawing up a new statement record or obtaining a voluntary production form).

Centring on the exclusionary rule for illegally obtained evidence and the framework for assessing derivative evidence (fruit of the poisonous tree) established by Supreme Court en banc judgment 2007Do3061, this brief analyses how the seriousness of a procedural violation and the requirements of attenuation or severance of the causal link may be challenged.

Material to check

First, records comparing the application for the first search-and-seizure warrant, the warrant as issued and the seizure record with the second request for supplemental investigation and its list of questions.

Second, the questions and answers in the interrogation records, and the video recordings, showing whether, at the time the second statement or voluntary production was made, the investigative agency presented the items unlawfully seized in the first stage or used them as the basis for pressing questions.

Third, records concerning the time interval between the first procedural violation and the acquisition of the derivative evidence, whether the assistance of defence counsel was available, and whether an independent third source of information existed.

Possible readings

The Prosecution Service's reading argues that, even if the first seizure procedure was partly defective, the illegality is attenuated or severed, and the derivative evidence is admissible, where the suspect or witness was thereafter informed of the right to remain silent in the presence of defence counsel and voluntarily made a statement or produced materials.

The defence reading counters that, in cases where the second investigative lead or the questioning itself would have been impossible without the items unlawfully seized in the first stage, recognising a break in the causal link merely because a subsequent agency or procedure gave formal notice would reduce the constitutional warrant requirement and Article 308-2 of the Criminal Procedure Act to empty shells.

What the decisions held

Supreme Court en banc judgment 2007Do3061 delivered 15 November 2007 held that not only evidence collected without following due process but also derivative evidence obtained on the basis of such evidence cannot, in principle, be used as evidence of guilt, and that, by way of exception, for the causal link between the procedural violation and the derivative evidence to be regarded as attenuated or severed, the derivative evidence may be used as evidence of guilt only where exceptional circumstances are established in which the violation does not infringe the substance of due process and exclusion would instead undermine the ideal of criminal justice.

Supreme Court en banc decision 2011Mo1839 dated 16 July 2015 held that where, before the search and seizure of electronic information is completed, electronic information relating to a separate suspected offence is discovered by chance in the course of a lawful search for the relevant electronic information, further searching must stop and a separate warrant must be obtained, and that, absent special circumstances, appropriate measures to protect the interests of the person from whom the items were seized must be taken, such as guaranteeing that person's right to participate and delivering a list of the seized electronic information. Supreme Court judgment 2018Do18866 delivered 1 June 2023 held that evidence unrelated to the facts constituting the suspected offence on which issuance of the warrant was based may not be seized and may not be used as evidence of guilt without a separate warrant, and upheld the court below, which had treated the two seized memo sheets and the other evidence collected on the basis of those memo sheets all as illegally obtained evidence.

Practical checklist

First, before the derivative evidence (statement records or articles voluntarily produced) was obtained, did the record contain an independent investigative lead unrelated to the material unlawfully collected in the first stage?

Second, during interrogation, were the items unlawfully seized in the first stage, or printouts of them, presented directly to the suspect or witness in order to elicit statements?

Third, was the first procedural violation a mere minor error of form, or an infringement of the essence of due process, namely the warrant requirement, the right to participate or the relevance limitation?

Fourth, did the Prosecution Service prove, by specific records, the exceptional circumstances for a break in the causal link with respect to the derivative evidence?

Glossary

Derivative evidence (fruit of the poisonous tree) and the fruit-of-the-poisonous-tree doctrine: the principle that evidence derivatively obtained on the basis of unlawfully collected primary evidence inherits the illegality of the primary evidence and is therefore inadmissible.

Attenuation or severance of the causal link: the standard for identifying the exceptional cases in which derivative evidence may be used as evidence of guilt, by considering all circumstances relating to the collection of the derivative evidence as a whole and comprehensively, centring on whether the causal link between the collection of the primary evidence and the collection of the derivative evidence has been attenuated or severed.

Sources and limitations

This brief is based on Article 308-2 and other provisions of the Criminal Procedure Act as checked on the National Law Information Center as of 15 October 2026, and on Supreme Court en banc judgment 2007Do3061, en banc decision 2011Mo1839 and judgment 2018Do18866.

This is general research material and not legal advice on any individual case.

Points left open

A further issue that remains is whether a good-faith (good intentions) defence is available where, in supplemental investigation after a transfer between agencies, the second agency claims that it was unaware of the procedural defect of the first investigative agency.

When to reconsider

This brief will be reviewed again once further Supreme Court judgments accumulate on the standard for a break in the causal link for derivative evidence across multiple investigative agencies.

Statutes referred to

• 형사소송법 제199조, 제215조, 제244조의3, 제307조, 제308조의2, 제312조
• 헌법 제12조 제1항·제2항·제3항

Decisions referred to

• 대법원 2007. 11. 15. 선고 2007도3061 전원합의체 판결 · Decision ledger
• 대법원 2015. 7. 16. 자 2011모1839 전원합의체 결정 · Decision ledger
• 대법원 2023. 6. 1. 선고 2018도18866 판결 · Decision ledger

Verification status

The text of Articles 199, 215, 244-3, 307, 308-2 and 312 of the Criminal Procedure Act and the texts of Supreme Court en banc judgment 2007Do3061, en banc decision 2011Mo1839 and judgment 2018Do18866 were checked against the National Law Information Center as of 15 October 2026. The judgment in 2018Do18866 was checked again on 21 October 2026. This brief cites only the judgments listed among the judgments it discusses.