It includes
Barak Obama
Susan Rice
Ben Rhodes
Valerie Jarrett
Maybe a few more
At DIA it would have been Clapper and at CIA it would have been Brannen
In the FBI it could have been Comey, McCabe , Strzok or Bill Priestap
This is not a difficult task to sort out.
Everyone cleared to participate in FISA have a Top Secret clearance and the NDA for that level of clearance should include a clause where they are obligated to be deposed for mishandling or espionage related activities while under polygraph testing
Absent political coverup, sandbagging or official DOJ / FBI obstruction the investigation should be fast and effective
Expect this to happen after the FBI/DOJ small group has been deposed under oath by Congress