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. The broadcaster's president, Deborah Turness, announced the probe in an internal memo on Friday. Williams has apologised for falsely saying on air that he was in a helicopter hit by a rocket-propelled grenade while in Iraq in 2003. Turness said on Friday the anchor had 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 , Newsday and ABC and is now at NBC, is leading the probe. 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. The remarks drew suspicion because during Katrina, there was relatively little flooding in New Orleans' French Quarter. Williams was staying at the city's Ritz Carlton Hotel, according to an NBC source. Captain 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. The body Scott saw was about four blocks from the RitzCarlton, which was surrounded by up to one metre of water, he said.