Mans is slippin and losing his confidence
There was a time ten years ago when Prigozhin would have ingested some wild isotope that basically nobody knows how to make, and died slowly in a hospital in horrible disfiguring fashion. Putin would have said nothing, Russian state TV would have made a couple of snide comments, and everyone would have understood and not done a goddamned thing.
Now he's feeling like he needs to emphasize it. Yes, we know you killed him, and we've moved on. It's not that we just didn't figure it out.