during then-

[Eugene2114]

Hi,
“While the letter is unsigned, a Senate Committee confirmed a decade after it was sent that it had come from the FBI during then-Director J. Edgar Hoover's five-decade-long leadership of the bureau.”

--To me, what the ‘during’ does there is it stresses that the 50-year-long leadership was unchanged for the whole period he was at the helm. Otherwise, a simple ‘the then’ would suffice. (?)

[Eugene2114]

Or it should read: "...from the FBI then-Director J. Edgar Hoover's (who lasted at the post for five decades) leadership of the bureau.”
And 'during' relates to the period of time the story embraces.
Anyway, does it make a comprehensible reading for you?

[Beeesneees]

Yes, the original makes sense. Your alternative doesn't, as if you were to use that version you are saying that the letter came from Hoover's leadership - Hoover's leadership cannot have written a letter.

The original indicates the letter was written by someone in the FBI at the time Hoover was in charge of the organisation.

I don't see how 'during' adds anything to the fact that it was a 50 year leadership at all.
It wouldn't matter how long the leadership was.
'during' simply indicates it was within Hoover's leadership.

'then-director J. Edgar Hoover' indicates that Hoover was in office when the letter was written but he is no longer Director.

The only thing the phrase 'then-director' adds is to clarify that Hoover's title at the FBI at the time was that of 'Director'. Otherwise it could be more simply stated:
“While the letter is unsigned, a Senate Committee confirmed a decade after it was sent that it had come from the FBI during J. Edgar Hoover's five-decade-long leadership of the bureau."
_________________
"Inside every old person is a young person wondering what happened."
Terry Pratchett

[Eugene2114]

Though I don’t think ‘the leadership’ can’t write a letter—they can if they’re given the leeway ;-)—your analysis is superb.
That ‘during then-’ and ‘Hoover's five-decade-long leadership’ combo was wheels within wheels to me.
Thank you so much.

[Beeesneees]