It’s always tricky to report on high-profile federal investigations that are in progress. But that’s no excuse for “NBC Nightly News” anchor Brian Williams, who delivered a report last night about the “Bridgegate” probe involving New Jersey Gov. Chris Christie (R). Williams said that “federal charges are now ruled out” for the embattled governor, who is regarded as a serious contender for the Republican presidential nomination in 2016.

As reported in the Asbury Park Press today, however, NBC News has backtracked on this information. “An unscripted line of our Nightly News report was imprecise and implied that a final decision had been reached,” noted NBC News spokeswoman Erika Masonhall, according to the newspaper.

Indeed, the Williams report went much further than a highly cited story by WNBC-TV investigative reporter Jonathan Dienst. Here’s the first paragraph of that story:

The U.S. Justice Department investigation into Gov. Chris Christie’s role in the George Washington Bridge lane closure scandal has thus far uncovered no evidence indicating that he either knew in advance or directed the closure of traffic lanes on the span, federal officials tell NBC 4 New York.

Bold text highlighted for an important reason — the nine-month-old probe hasn’t yet concluded and “no final determination has been made,” noted Dienst’s report, which also carries the bylines of Joe Valiquette and Pete Williams.

A thread of irony runs through NBC News’s overzealous depiction of Christie’s clean hands. After all, it was MSNBC, NBC’s sister cable-news outfit, that blasted out Christie-scandal reporting and no small amount of speculation when news broke in January that a top Christie aide, Bridget Anne Kelly, had helped orchestrate the closure of two access lanes to the George Washington Bridge in September 2013 — perhaps an act of political payback against a New Jersey mayor who didn’t endorse the governor for reelection. When that story line emerged, MSNBC’s Chris Matthews called the goings-on “Nixonian.” Others on MSNBC went on at length in attempts to make sense of Christie’s denial of personal involvement and the actions of his subordinates.

Today one critic wondered how Brian Williams could clear Christie in his newscast yet Matthews couldn’t find time to do likewise on his MSNBC show. A guess: Matthews and his MSNBC colleagues won’t report this story until they get a signed affidavit of Christie’s full clearance.

Update (7:58 p.m.): On the Friday-night newscast of “NBC Nightly News,” Williams corrected the record:

We may have added confusion to some complex reporting last night — and it has to do with New Jersey Governor Chris Christie and the multiple investigations underway into so-called “Bridgegate,” when Christie surrogates allegedly ordered politically motivated lane closures on the busiest bridge in the world. The state of play is this: The Feds have SO FAR found no grounds for charges — no involvement of the Governor himself. Both the federal and state investigations continue.