El testigo refirió los hechos.

Because referir is a stem-changing -ir verb. In the preterite, many stem-changing -ir verbs change e → i only in the third person singular and plural.

So the pattern is:

• yo referí
• tú referiste
• él/ella/usted refirió
• nosotros referimos
• vosotros referisteis
• ellos/ellas/ustedes refirieron

That is why this sentence has refirió.

Refirió is the preterite tense, third person singular.

The preterite is used for a completed action in the past. Here, it presents the witness’s statement as a finished event: the witness gave their account.

If the sentence used refería, that would be the imperfect, which would suggest something ongoing, habitual, or backgrounded.

Not always. This is a very common learner trap.

In this sentence, referir means something like:

• to relate
• to recount
• to report

It is more formal than everyday to tell.

If you want the sense of English to refer to, Spanish often uses referirse a:

• Me refiero a eso = I’m referring to that

So in El testigo refirió los hechos, referir does not mean to refer in the usual English sense.

Yes. Referir in this sense sounds formal, literary, or legal.

In more everyday Spanish, you might hear:

• contó los hechos
• relató los hechos
• explicó lo ocurrido

Using refirió fits very well in police, court, or official written language.

Yes. Testigo is a common-gender noun. That means the noun form stays the same, and the article tells you the gender:

• el testigo = a male witness
• la testigo = a female witness

So testigo itself does not change to testiga in standard usage.

Because the sentence is talking about specific facts/events, not facts in general.

Spanish often uses the definite article when the speaker and listener are understood to know which facts are being talked about. In legal or official contexts, los hechos is very common and often means:

• the facts of the case
• the events being described
• what happened

So the article los makes the phrase sound specific and definite.

It can carry both ideas, depending on context.

In legal and formal Spanish, los hechos often means:

• the events that took place, and/or
• the facts as they are being stated in testimony

So it is broader than just the everyday English word facts. In a witness statement, it often points to what happened as recounted in an official way.

Because los hechos is the direct object, but it refers to things/events, not people.

The personal a is mainly used before specific human beings (and sometimes personified animals or very personalized beings):

• Veo al testigo
• Escucharon a la víctima

But here the object is los hechos, which is not a person, so there is no personal a.

The accent mark shows the correct stress: re-fi-RIÓ.

Without the accent, the spelling would not correctly show the pronunciation. In Spanish verb forms like this, the written accent helps indicate that the stress falls on the final syllable.

So the accent in refirió is a normal spelling feature of the form, not an optional mark.

Yes, but El testigo refirió los hechos is the most neutral and straightforward order: subject + verb + object.

Spanish word order is more flexible than English, so other orders are possible for style or emphasis, for example:

• Los hechos los refirió el testigo
• Refirió los hechos el testigo

But the original version sounds the most neutral and natural in isolation.