By David Bauder, Television Writer

NEW YORK (AP) --

NBC News has assigned the head of its own investigative unit to look into statements that anchor Brian Williams made about his reporting in Iraq a dozen years ago, an episode that's ballooned into a full-blown credibility crisis for the network.

NBC News President Deborah Turness announced the probe in an internal memo on Friday. Williams has apologized for falsely saying on the air that he was in a helicopter hit by a rocket-propelled grenade while in Iraq in 2003, and Turness said Friday the anchor expressed his regrets to his colleagues for the impact the episode has had.

"As you would expect, we have a team dedicated to gathering the facts to help us make sense of all that has transpired," Turness wrote. "We're working on what the best next steps are."

Richard Esposito, who has worked at the New York Daily News, New York Newsday and ABC and is now at NBC, is leading the investigation. There was no immediate word on whether Williams would anchor NBC's "Nightly News" on Friday.

Questions were also raised about statements Williams made on coverage of Hurricane Katrina, which was one of his proudest moments at NBC. In a 2006 interview with former Disney CEO Michael Eisner, Williams twice referenced seeing a body float down a street in New Orleans.

"When you look out of your hotel room window in the French Quarter and watch a man float by face down, when you see bodies that you last saw in Banda Aceh, Indonesia and swore to yourself that you would never see in your country," Williams said.

Several minutes later, Williams again talked about seeing the body as he discussed how it felt to cover the storm.

"I felt something get dislodged that changes the usual arm's length relationship between me and the stories I cover. These are Americans. These are my brothers and sisters. And one of them was floating by."

The remarks drew suspicion because during Katrina, there was relatively little flooding in New Orleans' French Quarter.

Williams was staying at the Ritz Carlton hotel in New Orleans, according to an NBC source who requested anonymity because the person was not authorized to speak on personnel matter.

Capt. James Scott, who was a police commander in the downtown area at the time of Katrina, said he saw a body floating along Rampart Street on the edge of the French Quarter. "It was floating with the water," he said.

The body Scott saw was about four blocks from the Ritz-Carlton, which was surrounded by up to three feet of water, he said.

Alex Brandon, a Washington-based photographer for The Associated Press, was working in New Orleans during Katrina and said there was enough water to launch a flat-bottomed boat from in front of the Ritz. He also said he photographed a dead body floating on Canal Street a few blocks from the Ritz.

The story originally called into question about Williams' wartime reporting experience has made him a subject of mockery, including a New York Post front cover that depicted him with a long Pinocchio's nose, over the headline "A Nose for News."

He's the leading man at the network's news division, whose nightly newscast has topped its rivals in ratings for the better part of a decade. As a frequent talk show guest and one-time "Saturday Night Live" host, his celebrity transcended the news division.

He apologized on the air Wednesday for telling his story about the supposed grenade attack as recently as last Friday on "Nightly News." He admitted that his helicopter was not hit by a grenade after war veterans had come forward to question the account, some even disputing whether Williams' helicopter was in a group that came under direct attack.

NBC News needs to look at not only Williams' story about the helicopter, which has changed in details as he's talked about it over the years, but whether anybody else at the network knew that he was spreading a falsehood and did anything about it, said Kelly McBride, an expert on ethics for the journalism think tank the Poynter Institute.

"He is the front man of 'Nightly News' and is seen as the primary arbiter of the facts," McBride said. "For him to get something wrong on something he was involved in casts doubt on his ability to get any facts right."

NBC News must also weigh his importance to the news division and the work he has done since taking over as top anchor from Tom Brokaw in 2004, she said. Brokaw, for his part, on Friday denied a published report that he had suggested Williams be dismissed.

"Brian's future will be decided by him and the executives of NBC News," Brokaw said.

That would be Turness and her immediate supervisor, Pat Fili-Krushel, who had seen "Nightly News" as a bright spot for the network as they tried to correct ratings problems at the "Today" show and "Meet the Press." NBC's corporate parents at Comcast would likely weigh in as well.

Meanwhile Friday, CNN said it was stepping back from its own report Thursday, quoting Rich Krell, a veteran who claimed to pilot Williams' helicopter in Iraq. Krell had said Thursday that the helicopter had taken small arms fire — if not a grenade attack — but said Friday that he was questioning his own recollections after being contradicted by other veterans.

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Associated Press writer Cain Burdeau in New Orleans contributed to this story.

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