The testimony of a witness constitutes, along with the testimony of the accused, the expert and the detained person, another means of producing evidence, the essence of which is the testimony of a person about facts important for decision-making in criminal proceedings. A witness always testifies about what they have perceived with their own senses.

A witness is a natural person different from the accused person, who was called (summoned) by an authority involved in criminal proceedings to give testimony on matters important for criminal proceediongs, which this person has perceived (experienced) by their senses, i.e. seen, heard etc. As such, a witness is irreplaceable by another person.

As long as joint criminal prosecution is being conducted, a co-accused person cannot be interviewed as a witness regarding the criminal conduct of another co-accused person, not even in case where they would testify regarding a criminal offense, for which they are not being prosecuted.

Witnesses can be adults, minors (including persons under the age of 15), as well as persons with mental and physical disorders. An aggrieved person may also be a witness, even though they are more invested in the outcome of the criminal proceedings than other witneses.

The Code of Criminal Procedure stipulates a general witness obligation, which includes:

• the obligation to appear on summons before authorities involved in criminal proceedings,
• the obligation to testify as witness about matters known to them regarding the criminal offense, its perpetrator and circumstances important for criminal proceedings.

The basic obligation of a witness is to appear on summons before authorities involved in criminal proceedings. The obligation to appear may be enforced by imposition of a procedural fine or the person may be brought in. The obligation to appear applies to everyone, i.e. also persons, who cannot be interviewed, and persons who have the right to refuse to testify. The only exception are persons enjoying privileges and immunities according to the domestic or international law.

The obligation of a witness to apper on sumons must be complied with in person due to the irreplaceability of witnesses; representation is not possible.

To obligation to testify as witness means to give a true account of everything the witness knows about any and all matters important for criminal proceedings, i.e. the criminal offense, for which the proceedings are conducted, its perpetrator, or any other curcumstances important for the proceedings. If the witness makes an untrue statement about a matter of a crucial importance for the decision or withdraws any such information, they may be subject to criminal liability for the criminal offense of perjury and false expert opinion.

There are certain exceptions from the obligation to testify, which implies that some persons are not obliged to testify (or are prohibited from testifying), however, they are obliged to appear on summons. These exceptions are justified primarily by public interest (interest in keeping certain facts secret) or by a private interest. These include the following cases:

• persons enjoying privileges and immunities according to the domestic or international law,
• persons who cannot be interviewed,
• persons entitled to refuse to testify,
• members of Parliament, senators and judges of the Constitutional Court; these persons have the right to refuse to testify only concerning facts which they learned in relation to the exercise of their official function and even after they cease to exercise those functions; this is their right which they are not obliged to invoke.

A witness also has the following obligations:

• to submit to examination of mental condition,
• to submit to a body examination,
• to tolerate taking of blood samples or other similar actions, unless such actions pose a danger to thier health, including the taking of biological material samples,
• to submit to actions necessary to ascertain the identity of a person, who was present at the crime scene,
• to write the necessary number of words, if necessary to ascertain the authenticity of one’s handwriting,
• to describe a certain person or object within the frame of recognition,
• to participate in supervised confrontation,
• to submit to participation in additional actions of criminal proceedings (e.g. investigative experiment, reconstruction, on-site verification, examination etc.).

Compliance with these obligations may be enforced by bringing the person in as well as by imposing a procedural fine. No other measures may be applied against a witness, i.e. incarceration or arrest for the purpose of performing a certain action.

A witness has the following rights:

• Right to repsect the prohibition of questioning (in case of confidential matters or obligation of secrecy).
  • The prohibition of questioning will be taken into account ex officio, unless, however, there has been a waiver of the obligation to maintain confidentiality of circumstances concerning confidential matters protected under a special legal enactment.
  • A witness must not be interviewed also in case their testimony would breach an obligation of secrecy imposed or recognized by the state, unless they were relieved of this obligation by the competent authority or the person, for whose benefit this obligation exists.
• Right to refuse to testify
  • The right to refuse to testify as witness pertains to the accused persons’s relative in a direct line, their sibling, adoptive parent, adoptive child, spouse, partner and and companion. A witness is furthermore entitled to refuse to testify if by testifying they would cause danger of criminal prosecution to themselves, their relative in the direct line, sibling, adoptive parent, adoptive child, spouse, partner or companion, or to other persons in a family or similar relationship, whose harm they would rightfully perceive as their own. The witness must be in each case advised on the right to refuse to testify before commencing the interview.
• Right to testify in their native language, or a language they know
• Right to have an interpreter present
• Right to legal aid
• Right to information on the whereabouts of the accused
• Right to keep the identity and likeness of the witness confidential
• Right to witness fee (travel expenses and lost profit)

If the established facts indicate that a witnessor a person close to them are likely to suffer harm to their health or other serious risk of violation of their fundamental rights, and if the protection of the witness cannot be reliably secured by other means, the authority involved in criminal proceedingswill take measures to conceal both the identity and appearance ofhte witness; name and surname and other personal data of the witness will not be written in the record, but they will be kept separately from the criminal file, and may only be reviewed by authorities involved in criminal proceedings in the case at hand. The witness will be advised on the right to request concealment of their appearance and sign the record under a fictious name and surname, under which they will continue to be registered. Where it is necessary to secure protection of such persons, the authority involved in criminal proceedings will take all necesary measures without delay.

A special manner of protection of witnesses and persons close to them is provided in a special legal enactment. Specific measures are provided in the Act no. 137/2001 Coll., on Special Protection of Witnesses and other Persons in Relation to Criminal Proceedings.