Have you checked out VA law/ case law regarding stipulations to evidence? Seems a lot of the call/texts could just be stipulated into admission, since the ability of potential witness to lay the proper foundation is pretty much a foregone conclusion. If Chris wants to examine Bella or Null over something in particular I guess they would need to be called. But insofar as proving or disproving the actual elements of what he is charged with idk what they would say besides essentially "yes, I was on the phone with you and you said you fucked your mom, as reflected in the recording."
Regarding text messages, Dalton v. Commonwealth (2015)
The Virginia court of appeals stated that while text messages constituted "writings", by themselves, simple screenshots of text messages are inadmissible hearsay, because by themselves it's not really possible to build adequate foundation for them. They're simply too easy to fake.
It's not quite binding case law because it was not actually part of the ruling. The court merely observed that the screenshots were admitted in error, but it was a "harmless error" because their inclusion did not have any meaningful effect on the verdict. Thus, while they agreed with the appellant that they were inadmissible, they found that it was not grounds for appeal in the case. Still, courts in Virginia will refer to Dalton.
It's for the same reason that in the 20th century you couldn't simply admit a typewritten document that says "My name is John Smith, and I murdered John Doe." Anyone could have written it on any typewriter.
Now, it's not impossible to build foundation for these things. For instance that typewritten document could have been found in the possession of John Smith, or an expert could analyze the particulars of the document and determine from the exact positioning of the struck characters that it was produced on John Smith's personal typewriter, but it's a tall order.
A screenshot of a text message is even worse because it's just bits and thus harder to determine provenance. If you're going to include a screenshot, the requirements for its inclusion are going to be very, very high.
The calls and letters are, of course, admissible with proper foundation, and the rules for this are very old, but they can't just be "thrown in". It takes work.
Following the "best evidence" rule, if you're going to include a handwritten letter, if an original exists you must produce the original. A photocopy is only admissible if the original is lost or destroyed. The keeper of the letter also must testify to its authenticity.
If you don't have these things, for instance if the original is destroyed and the recipient is dead, then you can admit a letter but you must build foundation another way. For instance you could have a handwriting expert testify that the writing matches Chris' handwriting.
So what I was saying wasn't that the prosecution couldn't attempt to include all these letters, but rather that they wouldn't bother, because the amount of work for something so unimportant would be unwarranted, especially since many of them could be thrown out anyway due to lack of relevance.
The phone call with Bella will be included because it's the best confession they have (unless Chris flat out confessed to the cops). The best evidence rule applies though, so they're going to have to put in work. For instance they're going to command Bella to produce the original, unedited call if possible.
They're also going to want Bella to give the best testimony possible for evidence that's so important. In the past, that would mean being physically present, though COVID has changed a lot. Restrictions have relaxed enough that I think they would at least want her to video conference from someplace other than her home -- home zoom calls are dicey because of the lack of a controlled environment.
In general courts have treated testimony in the same vein as best evidence. Best testimony would be the that the person is physically there, but if there are circumstances that prevent that, then you do a video call. If for some reason you can't do a video call, then you do a phone call. The important thing is that you do the best you can within the realm of reasonable possibility. You do not use a worse option merely because it's cheaper or more convenient.
I can't find a hard rule for this in Virginia, though in neighboring Maryland the courts have made this standard explicit after defendants made sixth amendment appeals concerning video testimony.
And, of course, you can use stipulation to include just about anything unless it's so bad that the judge complains, but if you're the defendant and your attorney lets the prosecution admit evidence as they please through stipulation, then you need a new attorney. 90% of the time a defense attorney's job is to be able to have a credible threat of making a trial a hassle, thus getting you better terms on your plea agreement.
(This is why having an attorney from a public defender's office is so bad. It's not that they're inherently bad attorneys, it's just that they don't have the *time* to make it painful for the prosecutor, and the prosecutor knows that. A good defense attorney builds a reputation for making a prosecution costly. Fortunately for Chris, Heilberg is not a PD and has a reputation to uphold.)