I found a part of the transcript that has a good illustration of the tactical considerations about calling witnesses, and what lawyers need to do in terms of anticipating need to use specific witnesses. It is in the trial transcript for Feb. 15, right before Jenn testifies, from about page 165-179.

CG raises an advance objection to Jenn's testimony because she is concerned that the Murphy plans to introduce double hearsay (Jenn's report of what Jay said that Adnan said). CG explains that the first mistrial took place before Jenn testified, and that the only information she has about Jenn's testimony is from the police statement with all that double hearsay in it. In the course of that explanation, she also explains that Jenn refused to talk CG's investigator because she had been instructed by the prosecution not to talk to the defense.

Then Murphy denies having said that to Jenn and interposes her own objection. The Judge assures Murphy that she does not believe Murphy would do anything improper, and that she realizes how these misunderstandings arise -- but that she will allow CG to ask Jenn about that on the witness stand if she chooses, and Murphy will be allowed to follow up on redirect.

Then CG says that she does intend to ask about that, and that she specifically added the investigator -- Drew Davis -- to her witness list so he would be able to testify to that incident, as possible impeachment of Jenn.

That discussion is also interesting because it really documents that Davis was actively employed to interview witnesses -- apparently CG had also asked Davis to write up a report or affidavit about Jenn's refusal to talk to him. ... so it's another glimpse into the overall trial prep strategy and investigative practices.