They need to investigate to find out if releasing classified (and higher) information is against the law? Yeah, right - that’s believable.../s
News alert!
Simply releasing classified information is only a crime if you have a security clearance. You agree to it when you are granted the clearance.
For everyone else, specific harm has to be shown. It's prosecuted under the Espionage Act, instead. And that's a pretty high threshold to meet, especially when all of the information released so far is not surprising.