(Kristi Kinard Suthamtewakul / via AP) Aaron Alexis (Kristi Kinard Suthamtewakul / via Associated Press)

A “U.S. law enforcement official.” “Two federal law enforcement officials who spoke on condition of anonymity because they were not authorized to discuss the investigation.” An “official.” “Reportedly.” A “senior law enforcement officer.”

Who knows who these people are. But one thing we do know is that they’re among the attributions that various U.S. news organizations have used to connect Navy Yard shooter Aaron Alexis to an AR-15, a military-style rifle. Some outlets reported that the AR-15 was alongside Alexis’s body following the rampage, and others alleged that he’d used it to kill people. CBS News settled on this formulation: “Sources say with that assault rifle, which is believed to be an AR-15, Alexis essentially was a sniper, able to easily target his victims from a very high vantage point.”

Whatever the case, a U.S. law enforcement official emerged this afternoon to say, in essence, that it’s all garbage. “We don’t have any information at this time that he had an AR-15 in his possession,” said the official. Only this “official” didn’t speak on the condition of anonymity because she was not authorized to discuss the investigation. She spoke on the record at a press conference to a big group of reporters. Her name is Valerie Parlave, the assistant director in charge of the FBI’s Washington Field office. (See press conference here or in video below.)

Parlave’s blast today will force uncomfortable newsroom conversations. We were hearing that from everyone, reporters and editors will lament, before trying to make their corrections as squishy as possible. And those discussions will take place just about everywhere. Which media organs, after all, didn’t fall for the AR-15 report? Perhaps the Erik Wemple Blog will seek to draw up a list. What is clear is that anonymous sources told a lot of reporters pretty much the same thing about Alexis’s weaponry. There was safety in numbers, too: Once a few outlets were reporting it, what’s the danger in getting in on the action?

Whenever tragedy strikes, it seems, news organizations turn to anonymous sources for bad information. It happened in Boston, when CNN reported that there had been an arrest in the marathon bombings; there wasn’t, yet. It happened in even larger fashion in Newtown, Conn., when a whole bunch of outlets reported falsehoods about the identity of the killer and his relationship to Sandy Hook Elementary school, among other developments.

Parlave today told the media: “In regards to the weapons used by Mr. Alexis, there has been a lot of information circulating in the media over the past day. Once again, we caution against obtaining information from unofficial sources and we ask that all inquiries be directed to the FBI.”

Have a look at how that brushback compares to an FBI statement from Boston: “Contrary to widespread reporting, no arrest has been made in connection with the Boston Marathon attack. Over the past day and a half, there have been a number of press reports based on information from unofficial sources that has been inaccurate. Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting.”

As MSNBC host Rachel Maddow noted on her show last night, “this is part of how we live now.” She was speaking, of course, about mass killings. Yet her simple words apply just as precisely to how media organizations screw up breaking news. Reliably, that is.

Continued FBI remonstration will not change things. Reporters are too addicted to their sources; their editors are too competitive; their sources are too willing to talk; the Internet loves information, even and especially anonymously sourced and bogus information. In the crush, we publish what we hear, not what we know.

Video streaming by Ustream

Visit NBCNews.com for breaking news, world news, and news about the economy