Indeed, I'm behind the curve here and I didn't realize what the actual fabrication allegation was. (Ironically I was up at the law library looking up something else instead of listening to Steve Bannon.) The prosecutor merely needs to have a reasonable belief that the text conversation took place. If someone else undertook to fabricate the conversation, then the prosecutor won't be sanctioned for it as long as he remains candid with the court as the investigation continues.
The complaint says the messages came from the roommate's phone. It does not say how they were given to law enforcement, but it was almost certainly via a forensic dump of the phone. If you don't do it that way, you have all kinds of evidence problems later. While the roommate could have shown the interrogators the conversation on the screen at first, the immediate next step would be to dump the phone and preserve the evidentiary record. Again, since this is a high-profile prosecution, it is quite likely the text message traffic was verified according to the dump before filing charges, although this would not necessarily reveal all tampering. Ultimately, if the authenticity of the conversation is in question, the SMS traffic can be obtained from the carrier and would reveal any attempt to use a burner phone or to alter the message or metadata.
Technical means aside, the motive for such fabrication remains cloudy.
If the messages are recovered from the roommate's phone, any fabrication would possibly have occurred on that phone and been undertaken by the roommate. That makes them an accomplice and subject to additional charges of obstruction of justice. Romanticism aside, it seems that this is something the roommate would do only if they were actually embroiled in it much more extensively and were seeking to create a false appearance of their own lesser involvement.
If you assume the conversation was fabricated, it still doesn't make sense. Why create a false trail of evidence that admits to the murder and connects to the physical evidence, but restates only the motive for doing so? By far the most common method of obstructing justice is simply to destroy evidence (or attempt to). In fact, that's what Robinson urges the roommate to do—a fact alleged in support of one of the counts of obstruction of justice. If you're going to fabricate a false trail of evidence, fabricate one that throws doubt on guilt. Say something like, "My grandfather's rifle was stolen, did you leave the door unlocked?" Or, "I went to UVU to hear Kirk speak, and now they all wrongly think I did it!"
Claiming a conversation was fabricated to admit to the crime but restate its motive away from right-wing talking points smacks of something the right-wing just really wants to be true—a scenario that would benefit the right-wing narrative but present no cognizable advantage for the alleged participants. There's no evidence that either Robinson or the roommate has any desire to shield any larger interest or absolve any larger political or social group. The fabrication theory amounts to nothing more than a conspiracy theory that the witness is hiding exactly what the right-wing commentators wanted the evidence to be, even if it makes no sense for the witness to do so.
