Why is the Pentagon not seeking to plug these leaks? They could very easily do that, with a threat of prosecution.
It could be that the leaks are intentional-to brace us for the bad news.
My guess is that the leakers aren't tied to the investigation at all, but going by hearsay. Hard to stop a leak of that kind. But to the WaPost, a janitor who once worked at the Pentagon's chow hall is a reliable source and a source "close to the investigation"