NEWARK, N.J. (AP) -- The U.S. attorney prosecuting allies of Gov. Chris Christie in the George Washington Bridge lane-closing scandal is known as a fierce litigator whose lengthy experience as a defense attorney exerts a balancing effect on his decisions as a prosecutor.

In this Jan. 11, 2014, file photo, traffic passes through the toll booths at the George Washington Bridge, in Fort Lee, N.J. (AP Photo/Richard Drew, File)

Equally evident is Paul Fishman's knack for avoiding speculation or expressing anything that could be considered an opinion. It's a quality that may frustrate reporters eager for a sound bite, but it reflects a deep understanding of his role and its responsibilities, former colleagues say.

The 16-month investigation into the closing of access lanes on the New Jersey side of the bridge, purportedly to punish a Democratic mayor for not endorsing Christie's re-election bid, culminated May 1 with the indictment of Christie's former deputy chief of staff and his top appointee to the Port Authority of New York and New Jersey, which operates the bridge.

Christie, who preceded Fishman as U.S. attorney, has denied any involvement in the lane closings and hasn't been charged with any wrongdoing.

At a packed news conference to announce the indictment, Fishman worked the crowd like a pro, eliciting more than a few laughs but refusing several times to be baited into offering his opinion on the indictment as representative of a larger "culture of corruption."

His job, Fishman said, is to determine "A, what happened; B, is it a federal crime; C, who's responsible and D, can we prove it beyond a reasonable doubt? That's it."

To people who have worked with him over the years, it came as no surprise.

"As a federal prosecutor, you're supposed to be neutral," said author and former state Attorney General John Farmer, who worked with Fishman as an assistant U.S. attorney in the early 1990s. "You're supposed to confine your comments to the four corners of whatever the charges are, or else you sound like a politician. Paul does a good job walking that fine line."

Some of his peers haven't always been as circumspect.

Last month, for example, Preet Bharara, U.S. attorney for the Southern District of New York, was scolded by a judge who wrote that his comments on indicted state Assembly Speaker Sheldon Silver, including that Silver practiced "the greedy art of secret self-reward," came close to crossing ethical boundaries.

In New Jersey in 2009, acting U.S. Attorney Ralph Marra was accused of making comments aimed at helping Christie, who had resigned several months earlier to run for governor, at a news conference announcing a large-scale corruption bust. A Justice Department investigation cleared Marra of wrongdoing.

Christie made corruption a stated priority and won well over 100 guilty pleas or convictions of public officials during his tenure.

Fishman has pursued corruption more selectively but has gained significant convictions in other areas such as mortgage fraud, identity theft and health care fraud.

Appointed by President Barack Obama in 2009, Fishman's roots in the public sector stretch back to the summer of 1980 when he interned in the same office he would eventually lead. After graduating from Harvard Law School, where he was managing editor of the Harvard Law Review, he joined the office in Newark as an assistant U.S. attorney in 1983 and by 1989 headed its criminal division, supervising 30 attorneys.

Farmer recalled in his first year being paired with Fishman for the sensational extortion and kidnapping trial of Kent Clark and Darryl DeVose, who had been fugitives for five years before being apprehended.

"I was new but Paul was the veteran on the team, and he did a phenomenal job," Farmer said. "It's a pretty intense environment, and you either come out of it best friends or never wanting to see each other again."

As is common for many assistant U.S. attorneys, Fishman switched to the private sector, where he spent more than a decade defending white-collar clients, often against the Christie-led U.S. attorney's office in Newark.

In one case, Fishman got charges dismissed against a Brazilian implicated in a large-scale international money laundering operation.

"He was someone all the junior attorneys wanted to work with, because he was working on interesting matters and because he was perceived as a good mentor and someone that you learned a lot from," said Lee Vartan, a New York-based attorney who worked under Fishman in private practice and, later, in the U.S. attorney's office.

Having experience defending clients can help a prosecutor anticipate what a defense attorney might do, but it also makes for the kind of measured approach Fishman appears to have taken with the bridge case, Vartan and others said.

"He's aware of the impact that bringing criminal charges has on someone's life, whether they're convicted or acquitted," said Robert Mintz, a criminal defense attorney who worked with Fishman in the U.S. attorney's office. "He wasn't going to succumb to public pressure to bring charges before his office was ready to proceed."

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