Correction: An earlier version of this article incorrectly identified Lisa Barsoomian's occupation. She is a lawyer at the National Institutes of Health.

Maryland U.S. Attorney Rod J. Rosenstein is pictured in his office. (Sarah L. Voisin/THE WASHINGTON POST)

Hours after then-Prince George’s County Executive Jack B. Johnson was arrested on suspicion of hiding cash bribes last fall, he stood at the Greenbelt federal courthouse and proclaimed his innocence.

“I just can’t wait for the facts to come out,” Johnson said. “I’m absolutely convinced I’ll be vindicated.”

Rod J. Rosenstein, 46, Maryland’s top federal prosecutor, stood before the microphones that day with no such bravado. “We don’t do fishing expeditions,” he said.

Rosenstein’s office had quietly spent more than five years building a case against Johnson (D). There were cooperating witnesses, documents seized in raids of homes and businesses, secret guilty pleas and Johnson’s voice on wiretaps.

The investigation was typical Rosenstein, say those who know him well: fair, methodical and detail-oriented. Even courtroom adversaries talk about the career prosecutor as if he were the real-life version of a Jimmy Stewart character.

“He is the poster child for the professional, competent, ethical and fair-minded prosecutor,” said defense lawyer Robert C. Bonsib, a former state and federal prosecutor.

Johnson, the highest-ranking official ensnared in the wide-ranging probe, ultimately admitted guilt and is facing sentencing. The case was so airtight that without a single trial, 14 others pleaded guilty, including Johnson’s wife — former County Council member Leslie Johnson — a former county housing official and three police officers.

Another sign of Rosenstein’s ability: He is one of only three U.S. attorneys — out of 93 nationwide — appointed by then-President George W. Bush who has been kept on by the Obama administration.

Colleagues say he keeps his politics out of the office. In 2007, Bush nominated Rosenstein to a federal appeals court. Maryland’s two Democratic senators blocked that move, portraying him as a carpetbagger and saying he should stay on as U.S. attorney.

One day this summer, Rosenstein faced a jury in federal court in Greenbelt. He held a miniature scales of justice.

A little theatrical flair to help convince jurors that defendant Jason Thomas Scott was a burglar and carjacker who had committed home invasions.

“The evidence in this case is so overwhelming, it practically breaks the scales,” Rosenstein told them.

Road to office

Rosenstein oversees 75 prosecutors, who work in Baltimore and Greenbelt, but he makes a point of personally trying about a case a year. His competitive side spilled out at Scott’s trial, as he walked out of the courtroom with defense lawyer Kobie Flowers to await a verdict.

“Don’t go too far,” Rosenstein said. Though he was smiling, he made clear he expected a quick conviction. After eight hours, the jury found Scott guilty of 11 counts.

Rosenstein grew up in the Philadelphia suburbs, and he graduated summa cum laude from the Wharton School at the University of Pennsylvania. After earning a law degree from Harvard in 1989, he got a job in the Justice Department’s public integrity section. He soon earned a reputation as a a top-flight trial lawyer.

A few years later, Philip B. Heymann, deputy attorney general in the Clinton administration, was looking for someone to serve as counsel. A career prosecutor whose judgment he trusted recommended Rosenstein.

Rosenstein quickly proved himself. “I would have trusted him with anything,” said Heymann, who has returned to Harvard’s law school as a professor. “If there was a case where I was worried there was a perception we were being unfair, I would trust him to do the right thing and to do the job.”

In the mid-1990s, Rosenstein landed in the middle of one of the most high-profile cases in years. Kenneth W. Starr named him to the team of prosecutors handling the Whitewater investigation into Bill and Hillary Rodham Clinton’s Arkansas business dealings. In 1997, Rosenstein began working as an assistant U.S. attorney in the office he would later lead.

A reorganization

In his downtown Baltimore office, Rosenstein keeps a pristine desk. On one recent visit, it held five papers organized in a neat cascade, and two coffee mugs, one with a DOJ insignia and another depicting Theodore Roosevelt.

He has a few photographs of himself with his wife, Lisa Barsoomian, 43, a lawyer at the National Institutes of Health, and their daughters, Julie, 11, and Allison, 9. There is also a photo of a young Rosenstein chipping away part of the Berlin Wall.

On prominent display behind his desk is a sign:

“Don’t tell me what I want to hear

Just tell me what I NEED TO KNOW.”

Rosenstein succeeded Republican Thomas M. DiBiagio, who was forced out by Justice Department officials after a stormy tenure during which he was accused of targeting Democrats in corruption probes for political reasons.

When Rosenstein took the job, the office lacked a sense of direction, current and former prosecutors said. Prosecutors took on a variety of cases, from gun crimes to drug cases and white-collar fraud.

“It was sort of the Wild West,” said Assistant U.S. Attorney Barbara Sale, chief of the criminal division. Rosenstein “imposed organization on us that was badly needed.”

Rosenstein took a few months to watch how things worked and to talk to former U.S. attorneys, judges, federal agents, defense lawyers, line prosecutors, police officials and state’s attorneys.

At the beginning of 2006, he reorganized the criminal division into five sections: national security, violent crime, narcotics, major crimes, and fraud and corruption. Each unit has a supervisor.

The investigation into Prince George’s corruption had begun in 2003, before Rosenstein took over. He said tipsters provided leads, and authorities investigated newspaper reports, including an article in The Washington Post that revealed that Johnson had awarded millions of dollars’ worth of contracts to friends.

“That case did not develop because we were out to get Jack Johnson,” Rosenstein said. “It developed because we were investigating a variety of different leads that ultimately led to Mr. Johnson and others.”

Rosenstein’s new fraud and corruption unit took it over.

Details of the probe had been kept so hush-hush that many of the colleagues of James A. Crowell, the assistant U.S. attorney who led the investigation day to day, didn’t know he was working on it. A special cipher lock had been installed on the door of Crowell’s office.

“So often, when you’re dealing with corruption, you rely on human intelligence. You need to have people on the front lines who are able to put it all together,” Rosenstein said. “It’s important to have responsibility and accountability concentrated in a single person.”

Rosenstein’s office also is prosecuting a separate bribery case against state Sen. Ulysses Currie (D-Prince George’s), who is on trial in federal court in Baltimore.

Although Rosenstein is probably best known in the Washington area for corruption cases, his office has compiled a notable record prosecuting gun crimes, street gangs, mortgage fraud, sexual predators, corrupt Baltimore police officers and users of child pornography.

He also created an asset forfeiture unit that in recent years recovered tens of millions of dollars from defendants, many of them contractors who defrauded the federal government.

Order at work, home

Rosenstein said he has no plans to leave his post and no intentions of running for public office. “My goal is to make this one of the finest U.S. attorney’s offices in the country,” he said. To the extent he can, he tries to maintain the same level of order in his home life that he does in the office.

“I don’t get home in time for dinner, but I’m usually home before the girls’ 9:30 bedtime,” Rosenstein said. He often stays up past midnight, working on legal briefs or returning e-mails from colleagues and law enforcement agents. Rosenstein usually walks his girls to their public school bus in the morning.

On weekends, he and the girls often go biking. The Barnes & Noble in downtown Bethesda is a favorite family destination.

Recently, Julie wanted to buy a Nook to read books. Rosenstein said that he and his wife are careful not to spoil their kids and that they were reluctant to let her make the purchase.

But, like a good lawyer, Julie presented her argument — that she would use money she had saved. “She made her case,” Rosenstein said.