But the investigation is moving at a gallop. On Friday, David Wildstein, a Christie appointee at the center of the scandal, said Gov. Christie knew about the lane closures as they were taking place, seeming to contradict the governor's previous statements.
The lane closings, from Sept. 9 to 13, have unleashed a burgeoning political scandal embroiling the Christie administration and setting back the governor's presidential ambitions.
Christie's standing in public opinion polls has dropped markedly since the release of e-mails last month suggesting some on his staff had a role in orchestrating the lane closings - in apparent retaliation against the Democratic mayor of Fort Lee for declining to endorse Christie for reelection.
"It looks fairly certain, based on what I've seen, that there was some abuse of power, but that doesn't give rise to a federal crime," said Kenneth Trujillo, a partner in Schnader Harrison Segal & Lewis L.L.P. in Philadelphia and a former federal prosecutor.
"Being a bully is not a criminal act," he said. "The danger in these kinds of investigations is that when you have embarrassing situations, people start covering up and either lie or destroy evidence."
On Jan. 9, Christie fired Bridget Anne Kelly, a deputy chief of staff, after disclosures of e-mails linking Kelly to the closure of two of three lanes to the bridge from Fort Lee. The closures caused massive gridlock, delaying police and emergency vehicles and forcing drivers to sit in traffic for hours.
Two other Christie allies at the Port Authority of New York and New Jersey, which operates the bridge, resigned in early December amid questions into the reason for the lane closures.
For months, Christie dismissed the incident, mocking the idea that anyone on his staff had anything to do with it - once saying that he "actually was the guy working the cones."
He's taking the issue very seriously now. Christie, a Republican, has hired prominent white-collar defense lawyer and former mob prosecutor Randy Mastro to conduct an internal review into the lane closings and respond to multiple investigations.
Others implicated have engaged top-flight criminal defense lawyers, too. It is unlikely the matter will be quickly resolved, given the avalanche of documents sought.
The U.S. attorney's investigation apparently has spread beyond the bridge scandal to encompass allegations involving Hurricane Sandy aid. Hoboken Mayor Dawn Zimmer said Lt. Gov. Kim Guadagno told her last year the city's flood relief was contingent on the city's signing off on a $1.3 billion development project being pushed by the law firm of David Samson, a Christie appointee who is chairman of the Port Authority of New York and New Jersey. Guadagno has denied the allegations.
White-collar defense lawyers say that at this stage, it is unlikely Fishman and his staff know with any certainty whether federal crimes were committed.
But the investigation passed an important threshold Jan. 23, when a federal grand jury sitting in Newark issued subpoenas for records of the Republican State Committee and the Christie reelection campaign. That by definition makes the matter a criminal investigation.
"The potential subjects [of the investigation] are lawyered up, and there are subpoenas going out and lawyers are going in to talk with the government, and there are attempts to narrow the subpoenas - it will take months to get a hold of all the e-mails and correspondence," said Marc Raspanti, a white-collar defense lawyer and former Philadelphia assistant district attorney is a partner at Pietragallo Gordon Alfano Bosick & Raspanti L.L.P.
"What I would do as a former prosecutor is get every scrap of paper," he said.
Christopher Hall, a former federal prosecutor who chairs the white-collar defense practice at Saul Ewing L.L.P. in Center City, said federal prosecutors could use a civil-rights-era statute making it a crime to engage in a conspiracy to deprive someone of their right to vote.
If it can be shown that officials in the Christie administration lashed out against Fort Lee Mayor Mark Sokolich because he chose not to endorse Christie, in effect supporting Christie's opponent, Democrat Barbara Buono, then the statute might apply, Hall said.
"Did two or more people seek to retaliate against individuals in their exercise of the right to vote? You would have to show that was the motive in the bridge closings," Hall said.
He added that prosecutors also might be seeking to determine whether federal mail and wire-fraud laws were violated when officials e-mailed one another about plans for the lane closings.
Anti-racketeering statutes might also come into play, as well as laws that bar the use of public property for campaign purposes.
Thomas H. Lee II, a former prosecutor in the U.S. Attorney's Office in Philadelphia and now a white-collar defense lawyer at Dechert L.L.P., said Fishman's office would likely be looking at whether federal funding for the bridge establishes a federal interest that would have been in some way harmed by the lane closing. On its face, he said, it is not obvious federal laws were broken.
Still, Trujillo said the risk in high-visibility investigations is that there will be charges simply because the federal net is so broad and because old enemies with grievances come forward with information.
"Once you have the U.S. attorney issuing subpoenas, it opens up a whole can of worms because their investigations tend to be wide-ranging and anyone who has ever felt slighted or injured will contact the prosecutors," Trujillo said.