El hombre asesinó al testigo.

Because Spanish uses the personal a before a specific human direct object.

In this sentence, the witness is the direct object, and it is a person, so Spanish adds a:

• asesinó al testigo

Also, a + el = al, so:

• a el testigo → al testigo

This does not mean to the witness here. It is just the normal grammar used with a specific person as the direct object.

Asesinó is the preterite (also called the simple past) of asesinar.

It is:

• 3rd person singular
• meaning he murdered, she murdered, or it murdered, depending on context

In this sentence, because the subject is El hombre, it means:

• the man murdered

The preterite is used for a completed action in the past.

The accent mark shows where the stress goes:

• a-se-si-NÓ

Without the accent, asesino would normally be stressed differently and would also look like another word:

• asesino = murderer / murderous (noun or adjective, depending on context)

So the accent helps show that asesinó is the past-tense verb form.

Both can be translated as killed, but they are not exactly the same.

• matar = to kill
• asesinar = to murder

So asesinó is stronger and more specific. It usually implies an intentional, criminal killing.

That means:

• El hombre mató al testigo = The man killed the witness.
• El hombre asesinó al testigo = The man murdered the witness.

Spanish usually needs an article before a singular countable noun in this kind of sentence.

So:

• El hombre = the man

Saying just hombre here would sound incomplete or unnatural.

The article tells us we are talking about a specific man, not just the idea of man in general.

Yes. That would also be grammatically correct, but it changes the meaning slightly.

• El hombre asesinó al testigo = The man murdered the witness
• Un hombre asesinó al testigo = A man murdered the witness

So:

• el points to a specific man, usually already known or identifiable
• un introduces one man, often new information

No. Testigo can refer to either a male or a female witness.

The noun itself does not change form:

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

So in your sentence, al testigo suggests the witness is male because it comes from a + el testigo. If the witness were female, you would normally say:

• La mujer asesinó a la testigo
• El hombre asesinó a la testigo

Notice that with a la, there is no contraction.

You do not pronounce it. In Spanish, h is normally silent.

So hombre sounds roughly like:

• OM-bre

In Spain, a more careful approximation would be something like:

• OM-breh

The stress is on the first syllable:

• HOM-bre

The normal, neutral word order is:

• El hombre asesinó al testigo.

That is:

• subject + verb + object

Spanish can sometimes change word order for emphasis or style, but this sentence is the most standard and natural version.

For example, other orders may be possible in certain contexts, but they sound more marked or literary. For a learner, this sentence is the best model to follow.

Yes. The verb form asesinó by itself can mean:

• he murdered
• she murdered
• sometimes it murdered

Spanish verbs often do not show the subject pronoun explicitly. The subject is understood from context.

In this sentence, the subject is clearly:

• El hombre

So here it specifically means:

• the man murdered

Because Spanish often leaves out subject pronouns when the subject is already clear.

Here, the subject is already stated:

• El hombre

So there is no need to add él.

In fact, saying:

• Él, el hombre, asesinó al testigo

would usually sound unnecessary unless you were emphasizing he.

Spanish is a language that often drops subject pronouns when they are not needed.