Earlier quoted context omitted.
Seymour Hersh has had a long and storied career, and he has made some very bold claims that later turned out to be correct. He's also, especially recently, made some very bold claims that so far have not turned out to be correct, whether because the truth just hasn't been revealed yet, or because Hersh was wrong or misled by his sources. It's also worth noting that Hersh - as with any journalist - is only as good as…
The thing that a good journalist would do is be skeptical of his crank sources and try to confirm them with reputable sources and evidence. He does neither. But a broken clock is right twice a day and a bad journalist can break two big stories in a career of publishing lies.
If you publish all at once, others can go and verify the details. The source is protected.
If you verify pre-publication, e.g., go to the diving school in Florida and ask too many questions, you (and the source) will be under surveillance in no time.