Does the D.A. have to produce all of their witnesses at the preliminary hearing?

Answer 1

No. As long as the DA can make a prima facie showing of sufficient evidence to bring the matter to trial, that's all that's needed to get past the preliminary hearing.

Multiple witnesses are often used to push the standard of proof at trial to the "beyond reasonable doubt" level, but that standard is not required at a preliminary hearing -- only prima facie showing that the prosecutor can present sufficient evidence to meet all elements of the offense.

Answer 2

That depends on the rules of the jurisdiction and whether or not hearsay is admissible. In general they must only prove a "prima facie" case -- meaning they need only produce some evidence for each element of the offense and that the Defendant committed it.

Answer 3

those that they have knowledge of,,,,