El testigo declaró y la policía escribió la denuncia.

Both are in the preterite, the Spanish tense used for completed actions in the past.

• declaró = he/she declared / gave a statement / testified
• escribió = he/she wrote

They are both third-person singular forms:

• declarar → declaró
• escribir → escribió

So the sentence presents two finished past events:

1. the witness gave a statement
2. the police wrote the report/complaint

The accent marks show that the stress falls on the last syllable:

• de-cla-RÓ
• es-cri-BIÓ

This is normal in many preterite forms of -ar and -ir verbs in the third person singular.

The accent also helps distinguish forms:

• declaro = I declare
• declaró = he/she declared

So the accent is not optional here; it is part of the correct spelling.

Because la policía is often treated as a singular collective noun in Spanish when it means the police force or the police as an institution.

So Spanish uses a singular verb:

• La policía escribió...

This is different from English, where the police usually takes a plural verb:

• The police wrote...

If you want to talk about several police officers individually, Spanish would usually say:

• Los policías escribieron la denuncia.

One extra detail: la policía can also mean the policewoman, depending on context. So context matters.

Usually, testigo keeps the same noun form for both genders. The article shows the gender:

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

So in this sentence, el testigo tells you the witness is male.

You may occasionally see testiga, but la testigo is the more standard and widely accepted form for learners.

Because declarar can be used on its own in legal or police contexts to mean:

• to give a statement
• to testify

So El testigo declaró is a complete idea by itself.

It does not have to mean a literal English-style declared something. In this kind of context, it often means the witness made a statement to the authorities.

You could expand it, for example:

• El testigo declaró ante la policía.
• El testigo declaró ante el juez.

But the shorter version is perfectly normal.

La denuncia usually means a formal complaint or report made to the authorities, especially the police.

Depending on context, it can be translated as:

• the complaint
• the police report
• the formal report
• sometimes the accusation, though that depends on context

In Spain, poner una denuncia is a very common expression meaning to file a police report / make a formal complaint.

So here la denuncia is not just any piece of writing; it is something more official.

Spanish uses definite articles more often than English.

Here, the articles mark the nouns as specific:

• el testigo = the specific witness
• la policía = the specific police force / police officer meant in the context
• la denuncia = the specific report/complaint

If the sentence were introducing them for the first time in a less specific way, you might see:

• Un testigo declaró...
• ...escribió una denuncia.

But with el/la, the sentence sounds like these are known or contextually identifiable people/things.