Breakdown of Niemand weiß, wer den Zeugen getötet hat.
haben
to have
wer
who
wissen
to know (a fact)
niemand
no one
Questions & Answers about Niemand weiß, wer den Zeugen getötet hat.
Why is it den Zeugen and not just den Zeuge?
Zeuge (witness) belongs to a group of masculine nouns that use n-declension. These weak nouns take an -n or -en ending in all cases except the nominative singular. Since the witness is the direct object (accusative) in this sentence, it becomes den Zeugen.
Could I use a form of kennen instead of weiß since a person is involved?
No, because the sentence doesn't say nobody is acquainted with the witness. It says nobody knows a specific fact: who committed the crime. Whenever you know a fact or introduce a subordinate clause (like one starting with wer, dass, or ob), you must use wissen, which conjugates to weiß for the subject Niemand.
Why does the verb hat go at the very end of the sentence?
The phrase wer den Zeugen getötet hat is an indirect question, which functions as a subordinate clause. In German, subordinate clauses require the conjugated verb (here, the helping verb hat) to be pushed to the very end of the clause.
Why is wer in the nominative case here? Doesn't the case change because it is the object of what nobody knows?