In this May 1, 2011, image released by the White House and digitally altered by the source to obscure the details of a document in front of Secretary of State Hillary Rodham Clinton, at right, President Barack Obama, second from left, Vice President Joe Biden, left, Secretary of Defense Robert Gates, right, and members of the national security team watch an update on the mission against Osama bin Laden in the Situation Room of the White House in Washington. (AP Photo/The White House, Pete Souza)

NBC News appears to be backtracking on a pivotal story about the killing of Osama bin Laden that appeared to bolster a controversial story by longtime investigative reporter Seymour Hersh in the London Review of Books. An “editor’s note” has been attached to the piece, saying the following:

Editor’s Note: This story has been updated since it was first published. The original version of this story said that a Pakistani asset told the U.S. where bin Laden was hiding. Sources say that while the asset provided information vital to the hunt for bin Laden, he was not the source of his whereabouts.

That’s a rather large qualification, one that stretches the confines of an “editor’s note” and reads more like a mammoth correction or perhaps a retraction.

It’s also a big moment in light of the story’s context. Hersh wrote in his exhaustive and much-challenged investigation of the May 2011 U.S. raid of bin Laden’s Abottabad compound that the official narrative of that operation and its run-up was pocked with lies. A key point: A “walk-in” source in August 2010 “approached” the CIA’s station chief at the US embassy in Islamabad, Hersh reported in his piece. “He offered to tell the CIA where to find bin Laden in return for the reward that Washington had offered in 2001,” writes Hersh.

That story conflicts with the line that the media had reported — namely, that U.S. intelligence had astutely ascertained bin Laden’s location through enterprise intelligence work. Officialdom’s claim that the courier discovery had led to the Abbottabad compound, reports Hersh, was actually a “cover story” to distract from a comment made in a rushed statement by President Obama following the killing. “The remark led to a new cover story claiming that the CIA’s brilliant analysts had unmasked a courier network handling bin Laden’s continuing flow of operational orders to al-Qaida,” notes the piece.

A whole bunch of debunking met Hersh’s allegations. The White House shouted it down. The National Security Council issued an on-the-record denunciation. Commentators and critics cited sourcing and logic problems.

Into the mix came NBC News, with a story that appeared to shore up Hersh’s contentions. Here’s the killer line from the piece: “Two intelligence sources tell NBC News that the year before the U.S. raid that killed Osama bin Laden, a ‘walk in’ asset from Pakistani intelligence told the CIA where the most wanted man in the world was hiding.”

The media world took note. Story after story cited NBC News as corroborating a key part of Hersh’s under-siege investigation. Even Hersh himself cited it. “What happened is we had a guy walk in. NBC last night about six o’ clock, put out that story saying it, and you hardly saw it today,” said Hersh in a Tuesday interview with “Democracy Now.

Carlotta Gall of the New York Times has written in support of Hersh’s reporting on the walk-in source. In a piece posted yesterday, Gall notes that her own research on the topic “tracks” with that of Hersh. “[I]t was indeed a Pakistani Army brigadier — all the senior officers of the [Inter-Services Intelligence] are in the military — who told the C.I.A. where Bin Laden was hiding, and that Bin Laden was living there with the knowledge and protection of the ISI.”

So, what to make of all this?

First, NBC News clearly sustained a heavy pushback operation over its original contentions. The story is anchored by four bylines — Matthew Cole, Richard Esposito, Robert Windrem and Andrea Mitchell. “They got leaned on,” said Hersh in an interview with the Erik Wemple Blog. Whatever the pressures, NBC News hastened to note that its reporting hardly buttressed the broad sweep of Hersh’s investigative report, which disputed a number of official story lines regarding the raid. “The NBC report is not contradicting the White House version and is not in agreement with Sy Hersh on most of the principal assertions that he’s making,” said Mitchell on yesterday’s edition of “Morning Joe.”*

Second, just how pivotal was the walk-in source? Perhaps somewhat, NBC News appears to be saying: “U.S. officials took pains to note he was one of many sources who provided help along the way, and said that the al Qaeda courier who unwittingly led them to bin Laden, Ahmed al-Kuwaiti, remained the linchpin of the operation,” notes the story.

Finally, the media dynamic unfurled by the Hersh story is fascinating in one key respect: Both NBC News and Gall of the New York Times have both come out and said they’d been pursuing this “walk-in” story for some time now. Here’s how NBC News describes its quest: “While NBC News has long been pursuing leads about a ‘walk in’ intelligence asset and about what Pakistani intelligence knew, both assertions were made public in a London Review of Books article by investigative reporter Seymour Hersh.” And Gall: “I was confident the information was true, but I held off publishing it. It was going to be extremely difficult to corroborate in the United States, not least because the informant was presumably in witness protection.” Should these outlets have acted sooner? Given the shakiness of NBC News’s post-Hersh account, maybe not.

In his interview with this blog, Hersh brushed away any concern over NBC News’s note. “The only thing I know is the position of the government now seems to be that the walk-in didn’t have to do with [the location of] bin Laden, the walk-in led them to the courier,” says Hersh. “I always thought it was the hard work of the CIA and enhanced interrogation that led them to the courier,” quips he, “They’ve changed the story…The theory I gather is they have to keep the courier story alive because it’s the one they make their money on.”

Summing up his view on the government’s denials, Hersh says, “It’s just a walking craps game: ‘Let’s just get through today and then we’ll worry about tomorrow,'” he says.

Of the followups by the New York Times and NBC News, Hersh says, “This is a story that was sitting there.” Credulous media organizations essentially repeated the stuff they were getting in official briefings, says Hersh. “The real story,” he says, “is about the failure of the media. It isn’t as bad as the collapse we did after Sept. 11, but this is a pretty serious failure.”

*Updated to add Mitchell quote.