The court documents also raise questions about the possible stifling effects of such investigations on press freedom, The Washington Post reported Sunday.
Newly released affidavits show Justice Department investigators used security badge access records to track the movements of Fox News chief Washington correspondent James Rosen and Stephen Jin-Woo Kin, the government adviser accused of being the source of the leaked information. The documents also detail how the government tracked phone calls between the two men and that a search warrant was used to obtain the reporter's personal emails.
The case bears many similarities to an inquiry by federal authorities revealed last week in which investigators obtained two months' of phone records for more than 20 telephone lines assigned to The Associated Press.
The revelation has drawn criticism from AP executives and First Amendment watchdogs for the broad scope of the subpoenas under which the records were obtained.
Such search warrants "have a severe chilling effect on the free flow of important information to the public," said Charles Tobin, a First Amendment lawyer. "That's a very dangerous road to go down."
The AP case shows the government expanded the techniques used in the 2009 investigation, said attorney Abbe Lowell, who is defending Kim on federal charges he disclosed national defense information.
"Individual reporters or small time periods have turned into 20 [telephone] lines and months of records with no obvious attempt to be targeted or narrow."
The U.S. attorney's office for the District of Columbia said prosecutors first sought the information through other avenues before subpoenaing the AP's phone records.