The only slightly remarkable thing is that it was 8-1 not 9-0, but Justice Thomas could not bring himself to vote to reverse. The op by Roberts makes short work (barely 4 pages) of that:
The State and the dissent advance various reasons why the jury might have discounted Boatner’s undisclosed statements. They stress, for example, that Boatner made other remarks on the night of the murder indicating that he could identify the first gunman to enter the house, but not the others. That merely leaves us to speculate about which of Boatner’s contradictory declarations the jury would have believed. The State also contends that Boatner’s statements made five days after the crime can be explained by fear of retaliation. Smith responds that the record contains no evidence of any such fear. Again, the State’s argument offers a reason that the jury could have disbelieved Boatner’s undisclosed statements, but gives us no confidence that it would have done so.