I think you answered your own question. They don't know where Heidi was killed and that would matter for jurisdiction. If that's never found out, I'm not sure how they would proceed but they
will based upon circumstantial evidence and they'll get a conviction on capital murder, imo. Hopefully our member lawyers will comment on this.
@riolove77 @gitana1
There's also the matter of the ligature/murder weapon. Plus we know they were searching for something between Austin and Houston, though no idea what it was. Any items that might be recovered would be tested for DNA, I assume.