Legal Question in Criminal Law in California

There is no specific rule against it other than that no one should be talking in the court room. Of course if there is a restraining order against the defendant and protecting the witness the defendant is not allowed to talk to the witness.

If the defendant has counsel, the D.A. is not allowed to communicate with him directly unless defense counsel consents. The same is true of the D.A.'s employees and agents. But it is not true of third-party witnesses whom the D.A. subpoenas.

As Mr. Shapiro noted, the witness must obey any court orders, and must also follow general rules governing behavior in the courtroom.