Even though there are laws requiring investigators to inform Senate/House Intelligence committees when senior members of the Executive branch are under surveillance, it appears those laws were not followed in the development of the case against CIA Director David Petraeus.
These statues came into play after Watergate, and were designed to keep intelligence committee members abreast of whom they could and couldn't call upon for needed testimony at certain times.
The fact that these rules weren't followed explains why the Senate/House intelligence committees were so taken aback to find that suddenly, the key figure for the Nov 15 Benghazi hearings, will not even be there.
Because of this breakdown in following the law, investigators did not keep lawmakers apprised of the growing investigation of Petraeus. And even though the investigation into Paula Broadwell, which eventually caught Petraeus, lasted for months, it was not portrayed to Congressional officials until about six hours before the CIA announced it.
One Congressional official made privy to the information at that time said, "It was portrayed to us as...if the FBI had stumbled across this."
This explains the shock of intelligence committee members who abruptly learned that Petraeus will not attend the Nov. 15 Benghazi hearing, in which high-ranking members of the Intelligence and State communities were to go on record, under oath, concerning Benghazi.