The extra security put in place last week by the NYPD stemming from a possible 9/11 terror threat remains in effect today, and New Yorkers will notice the subway bag checks and vehicle checkpoints.
New York City and Washington, D.C., tightened security last Thursday after intelligence collected from overseas
indicated a possible threat involving car bombs, as well threats to bridges and tunnels. The information indicated that three men would travel from Pakistan to the U.S. to carry out an attack.
The threat has been described as "specific" and "credible" but not confirmed.
Several federal officials say that four days of intense work have not generated any information to substantiate the threat information received Wednesday evening and made public Thursday.
A round-the-clock examination of flight records turned up several hundred names of interest, but interviews with those people failed to find any evidence of an actual threat.
The FBI and local police have looked for other indicators that a plot might be in the planning stages, such as large purchases of the chemicals needed to make car bombs, but no signs emerged of that either, officials say.
The heightened security in New York and Washington will be gradually tapered off starting tonight, after the evening commute. But it will not be simply stopped cold.
A joint FBI-Department of Homeland Security bulletin from Thursday said al-Qaida may be considering attacks that use improvised explosives packed in vehicles, similar to the "attempted attack on Times square" by Faisal Shahzad
in May 2010.
Al-Qaida may be aiming to avenge the death of Osama bin Laden and other key terror figures, the bulletin said.
Amid the heightened alert, threatening messages were posted on the White House Facebook page amid heightened alerts surrounding a possible 9/11 terror threat.
NBC New York was first to report the posts.
"We'll come back U.S.A. One day only 11/9/2011," said one message, featuring a photo of Osama bin Laden, using the date/month formula to reference Sept. 11.
"We'll come to u white house sooooooooooon," said another.
"We'll come back 11/9/2011 to kill u all," a third posting reads. The posts appeared briefly and were taken down.
Secret Service spokesman Ed Donovan said the agency referred the messages to its internet threat desk.
"They process it, make an assessment and determine what the next step is," Donovan said.
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Published at 6:24 AM EDT on Sep 12, 2011 | Updated at 6:34 AM EDT on Sep 13, 2011