Tom Maguire prolly has it right on the best way to investigate.
JustOneMinute: Be Careful What You Wish For: "However, if there is to be an investigation, here is the way to do it - give everyone involved immunity from prosecution for leaking classified info, but keep them open to perjury charges."

Tom got it from Michael Ledeen who got it from a friend.
Current officials who leaked can lie and risk jail, or 'fess up and resign (which is a reasonable consequense, if this program was so troubling to the leaker - resigning in protest has an honorable history).

Former officials will at least be identified."