I am currently reading Ali Soufan's "The Black Banners." To refresh the memory of some, or to inform others who don't know who he is, Soufan was the FBI's top Arabic-speaking agent, who was already on the trail of al-Qaeda's growth before the East African embassy bombings in 1998.
Well, the CIA felt "the need," as Soufan notes in the introduction, to redact/censor stuff that was already in the public record.
And, at times, this gets ridiculous.
In one chapter, describing the interrogation of al-Qaeda leader Abu Zubaydah, due to the details of the pages, we can tell just what the CIA insisted had to be blacked out. The first word in the chapter is "I," with Soufan talking about how he was packing a suitcase for a vacation when he was ordered off to Pakistan. Also censored are other individual words such as "we," "me," "my" and "us."
(Soufan is charitable in general in the book but has not a lot of good to say about the CIA.)