Guide to the Admissibility of Evidence and Trial Procedure in Criminal Cases

Based on 127 consultation cases · Updated October 4, 2026 · Translated from the Korean original.

Whether evidence may be used in a criminal trial depends on how it was collected and prepared, and on whether there was an opportunity to challenge the statements and contents in court. As a general rule, unlawfully collected evidence cannot be used, while some evidence is admissible only if it is confirmed in court or meets strict requirements for an exception.

People involved → Defendant → Prosecution → Court → Evidence is offered at a criminal trial → Was the evidence collected through unlawful procedures? → Yes Criminal Procedure Act Article 308-2 → Have the effects of the unlawful conduct and its link to the evidence been removed? → No → Does the evidence meet applicable trial requirements? → Yes → Generally cannot be used to prove guilt → May be admitted if requirements are met → Check how the evidence was obtained → Check whether secondary evidence came from unlawful evidence → Check statements and records → Check court confirmation and guarantees of reliability → Check proof of guilt → Check for independent support for a confession and proof of calculation facts

Key points

Evidence collected through unlawful procedures and secondary evidence obtained on the basis of that evidence generally cannot be used to prove guilt. However, the court may make an exceptional determination after considering all relevant circumstances, including whether the causal connection between the unlawful conduct and the collection of evidence has been severed (Criminal Procedure Act, Article 308-2 (형사소송법 제308조의2), Examples 5, 12, and 15).
A breath test conducted while a person is under unlawful arrest cannot be used as evidence if the effects of the unlawful arrest have not been removed, even if the defendant later requested a blood draw or consented to the use of the evidence (Examples 12 and 15).
Conversations recorded by a private individual are assessed differently depending on whether the person making the recording was a participant in the conversation or whether it was a conversation between other people. A secret recording of a private conversation between others must be distinguished from a recording made by a participant in the conversation (Protection of Communications Secrets Act, Articles 3, 4, and 14 (통신비밀보호법 제3조·제4조·제14조), Examples 7, 9, and 17).
For a suspect interrogation statement prepared by a prosecutor, issues include whether the form and contents of the record accurately reflect the statement made in court and whether the statement was made under circumstances that provide particular guarantees of reliability. One example holds that a suspect interrogation statement prepared by the police may be used as evidence only if the defendant or defense counsel acknowledges its contents in court (Criminal Procedure Act, Article 312 (형사소송법 제312조), Examples 11 and 23).
There is a precedent holding that a statement record is inadmissible if the defendant does not consent to its use as evidence when the prosecutor recalls a witness who has already testified at trial and obtains a statement retracting testimony favorable to the defendant.
The fact that a witness is abroad does not, by itself, make a statement record admissible as an exception. It is necessary to establish, among other things, that sufficient steps were taken to secure the witness’s appearance in court and that the record was prepared under circumstances that provide particular guarantees of reliability (Criminal Procedure Act, Article 314 (형사소송법 제314조), Example 16).
A defendant’s confession cannot be used to prove guilt if it is the only evidence. However, a document that continuously and mechanically records business transactions may serve as independent evidence rather than as a document confessing to the facts of a crime (Criminal Procedure Act, Article 310 (형사소송법 제310조), Example 25).
To estimate the blood alcohol concentration at the time of drunk driving using the Widmark formula, the underlying facts—such as the amount consumed, the time of drinking, and the person’s weight—must be strictly proven, and the various individual factors affecting the calculation must also be considered (Example 1).

Frequently asked questions

Q. Can evidence collected unlawfully never be used in a trial?

As a general rule, evidence collected unlawfully and secondary evidence obtained on the basis of it cannot be used to prove guilt. However, the court may consider the nature and degree of the unlawful conduct, the causal connection with the collection of the evidence, and other relevant circumstances to determine whether the case is an exceptional one that does not undermine the substance of due process.

Case 5, Case 12

Q. If I requested a blood draw after being unlawfully arrested, can the results be used as evidence?

Even if you requested the blood draw yourself, it is difficult to find that the causal connection between the arrest and the collection of evidence was severed if there are no circumstances showing that the effects of the unlawful arrest had completely dissipated and that your freedom of decision-making was ensured. In that case, the blood test results cannot be used as evidence. There is a precedent holding that this does not change merely because you consented to the use of the evidence.

Case 12, Case 15

Q. If I take part in a conversation and secretly record a call with the other person, can I use it as evidence?

A distinction is made between a participant recording their own conversation and recording a private conversation between other people. Even if a participant’s recording is not, by itself, unlawfully obtained evidence, it must meet the requirements for admissibility, including that the recording accurately reflects what was actually said.

Case 7, Case 9, Case 17

Q. If I deny in court what I said to the police, can the police statement be used as evidence?

Under Article 312(3) of the Criminal Procedure Act, as cited in the example, a suspect interrogation statement prepared by an investigative agency other than the prosecution may be used as evidence only if the defendant or defense counsel acknowledges its contents in court. The provision means that the statement is not admissible if its contents are not acknowledged.

Case 10, Case 11

Q. What happens if I signed a prosecutor’s record but dispute that it accurately reflects what I said?

The fact that you signed or affixed a seal to a record does not, by itself, establish that its contents match what you actually said. The example explains that if the defendant disputes the contents, whether the record is genuinely authentic in substance becomes an issue; it is also relevant whether a video recording or another objective method can prove that the record matches the statement.

Case 11, Case 23

Q. If a witness lives abroad, can their recorded statement be used in court instead of having them testify?

The fact that a witness lives abroad does not, by itself, make the statement record admissible as an exception. The court must consider whether all available means, such as confirming contact information and issuing a summons, were used to secure the witness’s appearance in court, and whether the record was prepared under circumstances that provide particular guarantees of reliability.

Case 16

Q. Can I withdraw my consent if I change my mind during the trial after agreeing to the use of evidence?

According to the example, an expression of consent to the use of evidence may be revoked or withdrawn before the examination of the evidence is complete, but withdrawing consent after the examination is complete does not eliminate admissibility that has already been established. There is a precedent holding that consent cannot be withdrawn after the examination is complete even when consent was deemed to have been given because the defendant did not appear at trial.

Case 13, Case 20

Q. Can I be found guilty based only on a confession and a notebook I wrote?

A confession cannot be used to prove guilt if it is the only evidence. However, a document that records business expense details as they arise, irrespective of the facts of the crime, may be recognized as independent evidence rather than as a confession, according to a precedent.

Case 25

Q. Can I be punished based only on a blood alcohol concentration calculated using the Widmark formula?

To estimate the blood alcohol concentration at the time of driving, the underlying facts for the calculation—such as the amount consumed, the time of drinking, and the person’s weight—must be strictly proven. Because individual factors affecting absorption and elimination in the body vary, whether the calculation alone is sufficient must be assessed in light of the specific circumstances.

Case 1

Relevant laws

Criminal Procedure Act, Article 308-2 (형사소송법 제308조의2)
Criminal Procedure Act, Article 310 (형사소송법 제310조)
Criminal Procedure Act, Article 312 (형사소송법 제312조)
Criminal Procedure Act, Article 313 (형사소송법 제313조)
Criminal Procedure Act, Article 314 (형사소송법 제314조)
Criminal Procedure Act, Article 318 (형사소송법 제318조)
Criminal Procedure Act, Article 215 (형사소송법 제215조)
Criminal Procedure Act, Article 216(3) (형사소송법 제216조 제3항)
Criminal Procedure Act, Article 146 (형사소송법 제146조)
Criminal Procedure Act, Article 148 (형사소송법 제148조)
Criminal Procedure Act, Article 149 (형사소송법 제149조)
Criminal Procedure Act, Article 159 (형사소송법 제159조)
Protection of Communications Secrets Act, Article 3 (통신비밀보호법 제3조)
Protection of Communications Secrets Act, Article 4 (통신비밀보호법 제4조)
Protection of Communications Secrets Act, Article 14 (통신비밀보호법 제14조)

Watch out for

Whether evidence may be admitted and whether that evidence alone is sufficient to establish guilt are separate issues. The credibility and probative value of evidence are assessed separately.
Consent to the use of evidence must be revoked or withdrawn before the examination of the evidence is complete. Reversing that decision after the examination is complete may not eliminate admissibility that has already been established.
The underlying facts required to calculate the Widmark formula, such as the amount consumed, the time of drinking, and the person’s weight, must be strictly proven.
A recording of a private conversation between other people may be treated differently from a recording made by a participant in the conversation, so the circumstances of the recording and the participants in the conversation must be distinguished.

By the numbers

These provisions on the Korean bar exam

형사소송법 제312조 · 17 past questions (Round 4, Round 5, Round 6, Round 7, Round 10, Round 11, Round 12, Round 13, Round 14, Round 15)
형사소송법 제314조 · 15 past questions (Round 3, Round 4, Round 5, Round 7, Round 8, Round 10, Round 11, Round 12, Round 13, Round 15)
형사소송법 제313조 · 11 past questions (Round 1, Round 4, Round 8, Round 9, Round 10, Round 12, Round 13, Round 14, Round 15)
형사소송법 제318조 · 5 past questions (Round 5, Round 9, Round 12, Round 13, Round 15)

Source: 변습 변호사시험 기출 데이터셋 (CC BY 4.0 · 공공누리 제1유형) · Practice on Byunsi

Added from public data; separate from the article text.

Source cases

This guide was compiled by AI from the following Korea Legal Aid Corporation consultation cases (in Korean).

This guide is general legal information about Korean law, not legal advice for your situation. For a specific case, consult a lawyer or the Korea Legal Aid Corporation (call 132 in Korea).