NEW YORK (CBSNewYork/AP) – NBC anchorman Brian Williams says he’s temporarily stepping away from his nightly newscast amid questions about his credibility.

In a message sent to NBC News staff and released by NBC on Saturday, Williams says it has “become painfully apparent” to him that his actions have made him too much a part of the news.

NBC Anchor Lester Holt will sit in for Williams while the networks deals with the issue.

“The open-ended nature of announcement suggests it could go deep in February and may be permanent based on what NBC executives find in their investigation of what transpired,” Associate Professor and Director of the Graduate Journalism Program at Quinnipiac University, Rich Hanley, told WCBS 880 Saturday evening.

Williams apologized Wednesday for telling the story a week earlier during a “Nightly News” tribute to a veteran he had befriended during a 2003 reporting trip to Iraq. Before expressing his regrets on the air, Williams did so online and in an interview with the newspaper Stars & Stripes.

He speculated online that constant viewing of video showing him inspecting the damaged helicopter “and the fog of memory over 12 years, made me conflate the two, and I apologize.”

His story had morphed through the years.

Shortly after the incident, Williams had described on NBC how he was traveling in a group of helicopters forced down in the Iraq desert. On the ground, he learned the Chinook in front of him “had almost been blown out of the sky;” he showed a photo of it with a gash from a rocket-propelled grenade.

The NBC crew and military officials accompanying them spent three days in the desert, kept aground by a sandstorm.

But in a 2008 blog post, Williams said his helicopter had come under fire from what appeared to be Iraqi farmers with RPGs. He said a helicopter in front of his had been hit.

Then, in a 2013 appearance on David Letterman’s “Late Show,” Williams said that two of the four helicopters he was traveling with had been hit by ground fire “including the one I was in.”

In the wake of the controversy, the network has launched an internal investigation.

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