Criminal law affords federal prosecutors a number of options to gain testimony, chief among them granting witnesses immunity from criminal charges for testifying before a grand jury. Immunized witnesses who refuse to answer questions can be jailed on contempt charges and held for more than a year. In civil proceedings, contempt charges can lead to even longer jail time.
"Immunity is very powerful" as an investigative tool, said former federal prosecutor Kenneth Trujillo, now a white-collar defense lawyer with Schnader Harrison Segal & Lewis L.L.P. in Philadelphia. "The witness can be held in contempt and jailed if they don't comply."
A similar tactic might be available to the New Jersey Legislature, but the situation is unprecedented, and lawmakers are sorting through their legal options, said Assemblyman John Wisniewski (D., Middlesex), cochair of the committee investigating the September traffic jams.
Traffic came to a standstill Sept. 9-13 in Fort Lee, a major access point for commuters traveling to New York, after officials of the Port Authority of New York and New Jersey closed two of three access lanes to the George Washington Bridge. Traffic jams delayed school buses, emergency vehicles, and police - for hours, in some instances.
E-mails subpoenaed by the Legislature and released in January suggested that senior Christie administration officials and allies in the Port Authority shut down the lanes in retaliation after Fort Lee Mayor Mark Sokolich, a Democrat, declined to endorse Christie's reelection bid.
Christie has denied any knowledge of the lane closing plan as it was being carried out, and the Port Authority officials involved in the lane closings have said it was part of a traffic study.
To date, the Legislature has subpoenaed 18 former and current officials of the governor's office and the Port Authority, as well as the Christie reelection campaign and the governor's office. Two - former deputy chief of staff Bridget Anne Kelly and the governor's former campaign manager, Bill Stepien - have invoked the Fifth Amendment. A third, David Wildstein, a Christie appointee at the Port Authority, turned over documents to the committee but declined to testify before the panel Jan. 9.
The subpoenas, and comments by public officials, suggest the investigations, at least for now, are focused on a handful of officials close to the governor. The U.S. Attorney's Office also appears to be looking into allegations by Hoboken Mayor Dawn Zimmer that the Christie administration tied flood relief money to approval of a development project there.
Experts on criminal law say that while the events leading up to the traffic jams suggest at least highly questionable behavior, it is not clear at this point that federal laws were broken.
If prosecutors conclude that a federal crime has been committed and key witnesses decline to cooperate, they typically work their way through the witness list in search of a person knowledgeable about the incident but not primarily responsible.
A key consideration is offering immunity to as few witnesses as possible. Prosecutors strive to make sure that people central to the crime are not immunized, said Thomas H. Lee II, a white-collar defense lawyer at Dechert L.L.P.
"It is a heavy club; it is extremely useful," Lee said. "But it has to be used carefully and with discretion so that you don't end up immunizing the really bad people and only going after the underlings."
There is often the potential for legislative and criminal investigations to conflict. But at these dual investigations unfold, Wisniewski said the legislative committee was taking pains to avoid hampering the U.S. Attorney's Office.
"We've made it clear every step of the way that we would steer wide of anything the federal authorities are engaged in," Wisniewski said.
Sometimes an immunity deal can backfire - as in the parallel 1980s investigations of the Justice Department and Congress of the Iran-contra arms deal engineered by Marine Lt. Oliver North, who served on President Ronald Reagan's national security staff.
Although Congress had banned financial aid for guerrillas fighting the Sandinista government of Nicaragua, North arranged to finance them from the proceeds of a weapons deal with Iran. Once the weapons deal was disclosed, Congress launched an investigation, and gave North immunity in exchange for testimony.
North later was convicted on federal criminal charges, but an appeals court overturned the conviction in 1992, finding that the trial judge had given insufficient consideration to the possibility that the evidence used by the prosecutors had been immunized and was not admissible.
The longest jail term for contempt is believed to have been served by former Main Line lawyer H. Beatty Chadwick. He was imprisoned for 14 years for failing to comply with a judge's order that he turn over $2.5 million in alimony to his former wife. Chadwick said he had lost his money in bad business deals and was released in 2009 only when the judge concluded that imprisonment had lost its "coercive effect."