Why wouldn't they?
Whoever knowingly and willfully communicates, furnishes, transmits, or otherwise makes available to an unauthorized person, or publishes, or uses in any manner prejudicial to the safety or interest of the United States or for the benefit of any foreign government to the detriment of the United States any classified information . . . concerning the communication intelligence activities of the United States . . . shall be fined not more than $10,000 or imprisoned not more than ten years, or both .
I dont know why a Grand Jury cant be empaneled to investigate a crime.....journalists called in to testify as to their sources...and if they refuse, then ala Judy Miller, off to jail.....!