They'd met nearly a decade earlier, through Rosenstein's wife-to-be, but they became friends while they were both Maryland assistants, said Greenberg, who spoke protectively of her colleague.
"He's got sound judgment. He is fair and impartial and strives to do the right thing," she said. "He does not view himself as Republican or Democrat, he views himself as the U.S. attorney."
Rosenstein returned to Washington for four years as a deputy assistant attorney general in the Justice Department's tax division, before he was selected to replace Maryland U.S. Attorney Thomas M. DiBiagio, who was forced out after a memo ordering his staff to produce three front-page indictments was leaked.
Morale was low when Rosenstein took over in the Baltimore office, Greenberg said, but he turned things around quickly. "He added resources that were sorely needed," she said.
His Project Exile program, a multi-agency effort to curb violent crime in the state, has been held up as a national model, as has his approach to Project Safe Childhood, which targets sexual predators. He's tackled gang violence, mortgage fraud and terrorism while showing "unprecedented cooperation" with state and local agencies, Gov.Martin O'Malleyhas said.
"Rod's a brilliant guy, and he's meticulous," said Steven H. Levin, who worked for Rosenstein as a federal prosecutor for three years before leaving to open his own firm in 2008. "He trusts the people who work for him … and he doesn't micromanage."
Levin said leak prosecutions by their nature are difficult, but he has faith that Rosenstein is capable of doing what needs to be done.
"If he can find the evidence that he and the agents are looking for, he's not going to be deterred by any potential politics of the situation," Levin said. "And he's fully capable of finding the evidence given his attention to detail… If there's a prosecution in this case, no one can argue with any degree of credibility that it's partisan."
A challenging case
It's rare for leaks to reach the prosecution stage for several reasons, including wide dissemination of material, a reluctance to subpoena reporters and a fear that additional intelligence information will be revealed in court. From 2005 through 2009, 183 potential leaks were referred to the FBI, according to agency statistics, leading to 26 investigations and 14 identified suspects — none of whom was prosecuted.
Prosecutions have ramped up under Obama, however. His administration has brought more leak cases than the three previous administrations combined, including the doomed case against former National Security Agency employee Thomas Drake.
Drake was accused of felony espionage for giving information to a Baltimore Sun reporter, but ultimately convicted of a misdemeanor computer violation. The case against him, which was filed in Baltimore but pursued by Washington prosecutors, collapsed last summer.
The vigor with which Obama's administration has gone after alleged leakers led people on either side of the political spectrum to cry double standard when pro-Obama leaks appeared in The New York Times.
"Could you have a more fawning story?" asked Gregory S. McNeal, a law professor at Pepperdine law school in California who specializes in national security. He referred to the Times "kill list" piece, which portrayed the president as a "student of writings on war by Augustine and Thomas Aquinas" who feels a "moral responsibility" for deadly actions.
It's a narrow universe that had access to such information, which should make it easier to identify the source, McNeal said. He suspects that the president himself authorized the disclosures, making them legal to share, but politically damaging.
And he trusts Rosenstein to reveal that if it's the case.
"When you look at his resume, he's not the kind of guy that you're thinking is going to be kowtowing to the whims of the White House or attorney general," McNeal said.
Rod J. Rosenstein:
Personal: Age 47. Married to an attorney, two pre-teen daughters, lives in Bethesda.
Education: Economics degree, University of Pennsylvania. Law degree, Harvard University.
Professional: Maryland U.S. attorney. Previous positions include associate independent counsel in Whitewater investigation and principal deputy assistant attorney general for the Department of Justice's tax division.