They were likely investigating the various journalists and their associates/bosses in the various news (and I use that word loosely) organizations so they could find as many people as possible who were involved in this and bring charges on them as well.
IMHO.
These kinds of crimes are like when you see a mouse (or cockroach) in your house. You know it’s not the only one.
It's hard for me to believe they are going to go after any news organizations. The Press is not exempt from secrecy laws, but they are given a lot of leeway.
The one case where Nixon tried to prevent the NY Times from printing the Pentagon Papers, he lost. (Amazing, horrible decision, IMHO, but still it happened.
If the DOJ starts arresting reporters for merely accepting tips then the story will flip 180* from "what this leaker did was wrong" to "see, Trump is trying to censor and shut-down the press".
Another thing is that the classification on this stuff was just reflexive. The thing the revealed was that Carter Page was going to be testifying to the SSCI. That's not much of a state secret when you get down to it.
I don't think even I (who hate these tard reporters) would approve of arresting a reporter for reporting that.
So, no, I don't think they took a bunch of times to figure out who else in ABC, NBC, CNN and the New York Times were involved, because they knew from the get-go it was too trivial a "secret" to try to bring any case against reporters and newspapers.
The Pentagon Papers decision said "the Government can not use prior-restraint to prevent publication of things they don't like". So the NY Times published legit top-secret stuff about our war effort, in THE MIDDLE OF THE WAR.
Even so, Nixon never sought to prosecute anyone at the Times or Post after the fact. Given all that I just can't believe the newsies are the targets.