BOSTON, Jan. 20 -- As local media maelstroms go, it had all the makings of a perfect storm.
An anonymous tip about a "dirty bomb" threat sent this city into a tizzy Wednesday evening, with nerves already frayed by a rush-hour snowstorm and speculation that an attack might be timed to coincide with the eve of the presidential inauguration in Washington.

Gov. Mitt Romney, at microphone, left inaugural festivities in Washington to return to Massachusetts.
(Chitose Suzuki -- AP)
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But in a briefing Thursday afternoon, Massachusetts officials said that although they had gathered new information about the four Chinese and two Iraqi nationals sought for questioning, an investigation had not increased their alarm or corroborated the tip.
It is still not known, they said, whether any of the people had even entered the country.
"There are some who would say that the information has a degree of unreliability to it," Gov. Mitt Romney (R) said in response to a reporter's question. Romney had dashed home from inaugural festivities after news reports of the threat broke.
"Could this be a hoax? Why, of course," he later added.
If so, some Bostonians and visitors wondered Thursday, had the frenzied response fueled a panic that officials said they were trying to avoid?
"It just seems like sensationalism and fear-mongering -- a real overreaction," said Erin Baldwin, 34, a graphic artist from San Francisco who arrived Thursday for a long weekend getaway with her husband.
Others said they were glad that precautions were taken. "It's kind of comforting that they took this thing seriously, even if it turns out to be nothing," said Eric Ronci, 23, a senior at Boston's Suffolk University.
Government officials in Washington said Thursday that they largely discount the notion that Boston was to be attacked, but they have not ruled it out. Some officials believe the tip was provided about one human-smuggling ring by a rival gang.
The tip traveled a circuitous route from the FBI's Joint Terrorism Task Force in San Diego to its counterpart in Boston, which shared it with local officials. The FBI notified two offices in the Department of Homeland Security, but not the headquarters. That led to confusion when local officials, reporters and members of the public began querying federal agencies, officials said.
On Wednesday, Homeland Security intelligence chief Patrick M. Hughes made several phone calls to state homeland security directors around the nation to explain the government's skepticism about the reported threat.
"This is just like thousands of other tips we receive all the time," one FBI official in Washington said. "We have to run it out and see if there's anything to it."
As news of the supposed threat broke Wednesday afternoon, politicians called for calm, while scrambling to show they were taking the threat seriously. Media reports described state officials gathering in a suburban bunker to plot strategy before an evening briefing from Boston Mayor Thomas M. Menino.
Romney, who has been stung here recently by newspaper reports of his broader political ambitions and frequent forays outside the state, said he returned to Boston to reassure residents. New Hampshire Gov. John Lynch (D) also returned to his state Wednesday.
The office of U.S. Attorney Michael Sullivan distributed the names and photographs of two Chinese men and two women that were immediately splashed across television screens Wednesday night, even as federal officials were playing down the validity of the tip. None of the named suspects appears on a terrorist or drug enforcement watch list, Sullivan said.
Jon Parris, an FBI spokesman, said late Thursday that authorities have added 10 more Chinese suspects, names that were developed as a result of the ongoing investigation. He said the information is still uncorroborated and the source is of unknown reliability and motive.
By that point, popular and acerbic radio hosts Howie Carr and Jay Severin were devoting their dueling drive-time call-in shows to the unfolding events. Sometime after the photographs were published, a public transit bus driver notified police that he thought he had dropped off two of those pictured in Somerville, a suburb north of Boston, the Boston Herald reported Thursday. But police descending on a Dunkin' Donuts franchise made no arrests.
"The interest continued to escalate, and there was a risk that there could be a public panic," Sullivan said when asked to explain the government's multifaceted response.
Staff writers Dan Eggen, John Mintz and Josh White in Washington contributed to this report.