It's not exactly clear where the misinformation started, but ABC News reported on the day of the shooting that Lanza was "wearing a bulletproof vest," according to "sources," and Fox 5 News's Ti-Hua Cheng "cited a law enforcement source that Lanza came into the school wearing black clothing over a bullet proof vest."
The media's inadvertent spreading of false information about the Newtown shooting is hardly without precedent. As author Dave Cullen told On the Media last week, much of what we initially heard about the Columbine massacre was flawed, too. "Two loner, outcast goths from the Trenchcoat Mafia went on a revenge slaying where they targeted jocks specifically to pay them back for years of relentless bullying," Cullen recalled. "Everything that I just said is wrong." Nevertheless, Cullen notes that "everyone, almost, still believes" that original narrative, as well as other details of the rampage — such as the girl who was supposedly killed for believing in God — that were later disproved.
Should the media focus less on "getting it first" and more on "getting it right"? Of course. That said, reporting in the field, in the midst of an unfolding event, is much more difficult than aggregating from the comfort and calm of one's cubicle, so we're not going to judge.