Learn Croatian: Saslušavši svjedoka, sudac je otišao kući. - Having heard out the witness, the judge went home.

It comes from the perfective verb saslušati (to hear out). To form this past verbal adverb, you take the infinitive, drop the -ti, and add -vši. This ending creates a word that means having done something in English.

Could I use the imperfective verb slušati to make this adverb?

Generally no. The -vši ending is almost exclusively added to perfective verbs like saslušati. This is because the past verbal adverb describes an action that was completely finished before the main action (otišao) took place.

Who is the one listening to the witness in this sentence?

The judge (sudac). A strict rule for using past verbal adverbs like saslušavši is that the person performing that action must be the exact same person as the subject of the main verb (je otišao).

Why does svjedok end in -a here?

The word svjedoka is the direct object of the listening action, so it needs to be in the accusative case. Because svjedok (witness) is a living male being (an animate masculine noun), its accusative ending matches the genitive ending -a.

Why do we use to say the judge went home instead of ?