Obama is in this up to his ears. But, even he isn't stupid enough to write anything down.
And there are plenty of people willing to fall on their sword rather than admit they discussed it with him. You can be sure they have been "promised they will be taken care of if they don't talk", which really means "they will REALLY be taken care of if they talk".
Implausible deniability. Obama is Rip Van Winkle.