Six thousand police officers, 1,173 police cars, 818 tons of concrete barriers and 39 miles of metal and wood barricades are what is needed to help protect Pope Francis on his visit to New York City -- and that's just the obvious stuff.

The NYPD is pulling out all stops -- including sophisticated technology -- to make sure the pope's visit is a safe one, not only for the pontiff but also for the hundreds of thousands of people expected to try to get close to him. Added to the task is the need to protect more than 200 dignitaries in town for the UN General Assembly.

An NYPD contingency of specialized officers is currently in Washington to monitor and learn from the security surrounding the pope before his arrival in the Big Apple, NYPD Commissioner William Bratton said Tuesday. The pope arrived Tuesday in Washington and makes his way to New York City tomorrow for a 39-hour visit.

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"We can see how he is acting with the crowds in Washington because he has this desire to mingle, which is very different from other popes," Bratton said at a news conference in Manhattan.

Bratton said he is confident of the "layers" of security being put in place to protect the pope and the crowds expected.

"This is an extraordinary infrastructure," Bratton said.

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His predecessor, Ray Kelly, said he expected smooth going during the pope's visit.

"I think it will go well," Kelly said. "The NYPD has a lot of experience doing this."

Monday, a joint-intelligence bulletin, released to law enforcement agencies days ago by the FBI, came to light warning that terrorists could use marked police, firefighting or other emergency units, impersonating officers and officials, to launch attacks during the three-city papal visit.

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NBC News obtained a memo with the bulletin, distributed by the Pennsylvania State Police Criminal Intelligence Center. NYPD Deputy Commissioner for Intelligence and Counterterrorism John J. Miller confirmed the bulletin Tuesday morning at an appearance with Bratton on "CBS This Morning."

To guard against impostors, Miller noted that "everybody's going to be challenged." He said all uniformed and plainclothes NYPD personnel -- including those attached to marked units -- will be questioned at every checkpoint.

And, Miller said of officers and officials when questioned: "You'd better know what you're talking about."

Bratton and Miller said there were no specific threats. Bratton joked the pontiff will have "6,000 guardian angels" -- meaning cops, watching him.

Speaking with reporters, Miller said a "lead squad" from the NYPD, FBI and Secret Service have been busy running down any report of a threat, which he said "have all washed out."

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"You get a combination of poison pens, anonymous calls where you never wind up knowing the motive," Miller said, "and just disturbed people who are actually making the threats themselves, are harmless and are usually under some sort of care or medication."

With Maria Alvarez,

Emily Ngo, John Valenti

and Darran Simon