good point. air could be that they use standard issue notebooks for meetings and they keep them all by policy. But I doubt it.
More likely as you say he kept these notes that show he was trying to be a good guy (or at least a less bad guy) in case the plan blew up.
"...Although there is no legal requirement that the government take notes of witness interviews, the accuracy of notes the government does take is critically important for multiple reasons. Foremost among those, the government is legally required to disclose to the defense exculpatory and impeaching information, and the government typically satisfies this burden by disclosing interview notes, interview memos (like 302s) that are based on notes, or both. In this regard, courts have found that the government can meet its disclosure obligations by turning over interview memos alone where the memos “contain[] all of the information contained in the interview notes,” and have also confirmed that where there are material differences between an agent’s notes and an interview memo, the government must turn over the notes themselves..."
Still kind of fuzzy, though. Does say the word "must" in there, which is a legally loaded word.