Breakdown of Conozco al ladrón que tiene esa barba.
tener
to have
esa
that (feminine)
al
to the
conocer
to know (people, places)
Questions & Answers about Conozco al ladrón que tiene esa barba.
Why do we use que for "who" here? Shouldn't it be quien?
In Spanish, que is the most common relative pronoun and can mean "that", "which", or "who". You can perfectly use que for people as long as it comes right after the noun it describes without a preposition (like de or con) in between. So here, que is the most natural choice for "who".
Why does the sentence say al ladrón instead of just el ladrón?
This is because of the "personal a". When the direct object of a verb is a specific person (like a thief), you must put an a before it. Since ladrón is masculine, the a combines with the word for "the" (el) to make the mandatory contraction al.
Why use conozco for "I know" instead of sé?
Spanish has two different verbs for "to know". Saber is used for knowing facts or knowing how to do something. Conocer is used for being acquainted or familiar with people, places, or things. Since you are talking about knowing a person, you use the yo form of conocer, which is the irregular conozco.
Why is it esa barba instead of ese barba?