It is someone else’s trial, but the risk is yours: what to do if you have been summoned as a witness

Juan Antonio Matiz Monroy — Lawyer, Universidad de los Andes · Specialist in Criminal Law, Universidad Sergio Arboleda · Professional licence 294.746 (C.S.J.)

Bogotá D.C. · Published: June 2026 · Reading time: 11 min

You saw something. Or a summons arrived asking you to give evidence about something you saw. They are two different doors into the same place, and at both the first reaction tends to be the same: not knowing what can and cannot be done.

That ignorance is not harmless. The anxiety of appearing without knowing what to expect degrades the evidence, testimony given badly proves nothing, and there is conduct —staying silent where the law requires a report, departing from the truth under oath— that is a criminal offence.

There are practices that reduce all three, and they are not tricks: they are lawful precisely because they protect the recollection instead of shaping it. This piece explains what they are and why they work.

1. Witness in a criminal trial in Colombia: the trial is someone else’s; the evidence is yours

People arrive at this situation by two routes. One is having witnessed something and not knowing whether anything has to be done about it. The other is opening an email or taking a call with a summons to give evidence about something already left behind.

In both cases the intuition is the same: this is someone else’s problem, and my part is to say what I saw. The first half is true: the proceeding is someone else’s. The second is not. Giving evidence is an act of your own, with duties and risks that are yours, not the accused’s.

Evidence is not given only at trial. It can begin with an interview by the judicial police or by a defence investigator, continue with a sworn statement and end in examination and cross-examination before the judge. Each of those settings has different rules, and not all of them protect the person giving evidence equally.

Nor is the witness left unprotected. If there are well-founded reasons to fear for their safety or that of their family, articles 133, 134 and 342 of the Criminal Procedure Code and the Prosecution Service’s Protection Programme allow measures to be sought. And you can consult a lawyer before appearing: being a witness does not make you a party, but nor does it oblige you to arrive without understanding what is going to happen.

2. What not knowing costs

The first cost is paralysis. Without knowing what can be done, the commonest reaction is to do nothing: not to write anything down, not to ask, not to take advice. Weeks pass and the recollection goes with them.

The second is anxiety, and it is not merely discomfort. Someone who comes to give evidence without knowing what they will be asked, who may question them or what happens if they cannot remember something, answers tensely, corrects themselves, contradicts themselves on minor details. The content may be true and the evidence still come out badly.

The third concerns memory, and it is the least intuitive. Ebbinghaus’s experiments and the literature that confirmed them show that forgetting is not linear: the greatest loss happens in the first hours and days. And research in the psychology of testimony —Elizabeth Loftus among others— shows that memory is reconstructive, not reproductive: each recollection is remade out of what was perceived and what was heard afterwards. That is why discussing the facts contaminates the recollection without anyone lying.

The fourth is criminal. Article 67 of the Criminal Procedure Code requires the reporting of offences that must be investigated of the authorities’ own motion —querellable offences are investigated only on the complaint of the victim—, and departing from the truth under oath is perjury (Ley 599 de 2000, art. 442). At the same time, article 33 of the Constitution guarantees that no one is obliged to give evidence against themselves, their spouse, their permanent partner or their relatives within the degrees it fixes. If what you saw implicates you, that guarantee exists and it is worth knowing beforehand, not in the room; the setting where that becomes concrete is the summons to questioning.

3. Familiarisation is not preparing the testimony

This is the distinction that orders everything else, and the one almost no one explains to a witness.

Familiarisation is knowing what is going to happen: who asks, in what order, what an objection means, what happens if you cannot remember something. It reduces anxiety and does not touch the content of the recollection. It is lawful. Preparing the testimony is working on the content: rehearsing answers, agreeing on words, deciding what it suits you to say. It contaminates memory, destroys spontaneity and exposes the person giving evidence.

The five practices that follow are familiarisation. All of them protect the recollection instead of shaping it, and that is exactly why they are lawful.

3.1. Write down what you remember, as soon as possible

Write what you saw in the first hours, in your own words and without polishing it. The reason is the forgetting curve: what is lost is lost early, and an early record preserves details that will no longer be there in a month.

Note also the date and time at which you write. That record does not replace your evidence and is not handed over without judgement, but it is the difference between remembering and reconstructing.

3.2. Do not discuss the facts with anyone

Every conversation about what happened introduces information that afterwards cannot be told apart from what was perceived. It is the post-event information effect, and it operates without anyone lying.

It also carries a procedural cost: prior conversations can be used to impeach your credibility in cross-examination (CPP, art. 403). Staying silent until you give evidence is not mistrust; it is protecting the source.

3.3. Say “I do not remember” when you do not remember

The pressure to help leads people to fill the gaps with inferences or with details suggested by the question. That is how sincere errors are born: no one lies and the evidence is false all the same.

“I do not remember exactly” is a complete answer and is worth more than a detail invented in good faith. A witness who acknowledges their limits also comes across as more credible than one who remembers everything.

3.4. Disclose every prior contact

Say who you spoke to before giving evidence, who interviewed you and what you were asked. Concealing it is what does the damage; saying it does not.

It matters because protection is not the same everywhere. Before the judge, article 392 of the Criminal Procedure Code prohibits misleading or leading questions and questions that suggest the answer; in a prior interview, outside the room, that prohibition does not operate in the same way. What was suggested there may have lodged itself in the recollection.

3.5. Disclose what affected your perception

The quality of evidence depends first of all on the quality of the original perception. Poor light, distance, angle, an event lasting seconds, acute stress: all of them degrade the record systematically.

Saying so does not weaken your evidence: it delimits it. An account that specifies from where and under what conditions something was seen withstands cross-examination far better than one that claims too much.

Honest but badly preserved testimony can be as damaging to justice as deliberately false testimony. And a person who has information about an offence and does not understand their legal position can take decisions that harm them —whether by speaking without guidance or by staying silent where the law requires otherwise.

4. Conclusions

The proceeding is someone else’s, but the recollection you will give evidence from is yours. That recollection is lost above all in the first hours and days, as Ebbinghaus’s forgetting curve shows. And it is contaminated by what you hear afterwards, as Loftus showed, without anyone lying. Prior conversations can be used to impeach your credibility (article 403). Departing from the truth under oath is perjury (article 442).

That is why two lawful practices protect you, in this order. First, write down what you perceived as soon as possible, with the date, the time and the conditions in which you saw it. Then, do not discuss the facts with anyone until you have written them down or given evidence. Saying “I do not remember” and disclosing every prior contact follow from those two. None of this is preparing the testimony: it is familiarisation with what is going to happen.

You are not alone in front of that summons. In the initial consultation we review what kind of summons you received and in which setting you will give evidence. We also consider whether your own position calls for caution and whether to seek protective measures under articles 133 and 134. Where the case requires it, the firm can provide criminal investigation advice, without touching the content of your recollection.

What people usually ask us

Legal and bibliographic references

• Ley 906 de 2004 — Código de Procedimiento Penal colombiano (arts. 67, 68, 133, 134, 342, 383, 384, 385, 392 y 403)
• Constitución Política de Colombia — art. 33 (derecho a no autoincriminarse)
• Ley 599 de 2000 — Código Penal, art. 442 (falso testimonio)
• Loftus, E.F. (1979). Eyewitness Testimony. Harvard University Press.
• Loftus, E.F. & Palmer, J.C. (1974). Reconstruction of automobile destruction. Journal of Verbal Learning and Verbal Behavior, 13(5), 585–589.
• Wells, G.L. & Olson, E.A. (2003). Eyewitness testimony. Annual Review of Psychology, 54, 277–295.
• Ramos, V. de P. (2019). Prueba testifical. Marcial Pons.
• Ebbinghaus, H. (1885/1913). Memory: A Contribution to Experimental Psychology. Teachers College, Columbia University.