Workers for the New York City medical examiner's office have begun sifting soil for possible human remains at a site near the World Trade Center where a chunk of airplane debris believed to have come from one of the 9/11 hijacked jetliners was found.

The aircraft part has been identified as a piece from a 767 wing, officials said Monday. NBC 4 New York, which first reported the finding in an alley near ground zero last week, has also learned the answer to the mystery of a rope that was found intertwined in the part — according to a law enforcement official, a detective who responded to the original call about the part last week tried to move it with a rope.

Authorities on Friday had said the rope might have indicated the part was lowered into the alley, but have since interviewed everyone who had contact with the part last week and have now answered that question. The official tells NBC 4 New York that the detective found the rope nearby and was trying to move the part to find a serial number or other identifying mark.

The NYPD also said Monday that a Boeing technician has confirmed that the 5-foot part is a trailing edge flap actuation support structure.

"It is believed to be from one of the two aircraft destroyed on Sept. 11, 2001, but it could not be determined which one," NYPD spokesman Paul Browne said.

On Sept. 11, American Airlines flight 11 hit the north tower at 8:46 a.m., and United flight 175 hit the south tower at 9:03 a.m. A FEMA graphic below shows that all the other plane parts in the immediate area were from flight 175.

Police and officials from the city medical examiner's office were on scene Monday preparing to sift the soil under the part for lost human remains. Officials said the part will be removed later in the week when that process is complete.

The part was found wedged between two buildings in a very narrow alley only about 18 inches wide between the rear of 50 Murray St. and back of 51 Park Place, the site where a mosque and community center has been proposed three blocks from ground zero.

The part bears a "Boeing" stamp, followed by a series of numbers.

The NYPD said the landing gear was found after surveyors hired by the property owner inspecting the rear of 51 Park Place called police on Wednesday. 

Most of the rubble from the 9/11 attack was cleared from the 16-acre site by the spring of 2002. Other debris, including human remains, has been found scattered outside the site, including on a rooftop and in a manhole, in years since.

Visitors to the National September 11 Memorial & Museum must now pay a $2 service fee to reserve passes online or by phone.

The fee went into effect last month, although there is no charge for admission to the memorial on the World Trade Center site. There's also no charge for same-day passes distributed on a first-come, first-served basis.

Family members of some 9/11 victims say the fee violates the memorial's mission.

"They're making money off the people that died. It's disgusting," Jim Riches, a retired FDNY deputy chief who lost his firefighter son, told the New York Post.

Memorial President Joe Daniels issued a statement Sunday saying that, "like other similar institutions, in order to help support the operational needs of the 9/11 Memorial we have implemented a service fee, solely for advance reservations."

The memorial's website says the reservation system is temporary until certain construction projects are finished. Tax-funded grants have paid for about $300 million worth of construction, and more than $400 million came from private donations.

The memorial opened in 2011, attracting about 7 million visitors so far to its two reflecting pools with waterfalls that outline the footprints of the fallen towers.

The foundation that runs the memorial estimates that once the project is complete, the memorial and museum will together cost $60 million a year to operate.

The museum is still under construction after an interruption involving a funding fight between the foundation and the Port Authority of New York and New Jersey, which owns the 16-acre trade center site. Officials have said that the failure to open the museum on time has thrown off the foundation's financial planning.

Visitors to the exhibit space will see portraits of the nearly 3,000 9/11 victims, hear oral histories and view artifacts such as a staircase World Trade Center workers used to escape.

The Associated Press

Related:

Politics on the side? US marks 11th anniversary of Sept. 11 attacks

PhotoBlog:360-degree-view of National 9/11 Memorial at dusk

Anna F. Curtis, journalism student at University of Missouri

Huge celebration in University of Missouri's Greektown. Champagne, fireworks, crowd surfing.

It started as a murmur, but quickly grew into a roar.

Chants of "U-S-A! U-S-A!" riccochted across the campus of The Ohio State University, building and evolving until it found a sympathetic audience near the famed Mirror Lake.  

If this were any night but Sunday, May 1, 2011, the revelry would have been chalked up to pent-up finals stress, or a successful sporting victory. But, this was not the case as college students across the country had the monster pulled from their their closets, and in Columbus, that meant a dip in the chilly water despite air temperatures and weather patterns that were less-than ideal.

Nearly ten years after 9/11, the children who watched the towers fall fill America’s colleges and universities, and on the evening the world learned of Osama bin Laden’s death, many took to the streets, celebrating the death of their generation's boogeyman. 

'There is finally justice'
Though they were young at the time - most were between the ages of 8 and 12 - many millennials cast the al-Qaida chief's death as a pivotal moment in their development. They came of age of age under the shadow of 9/11 and its vestiges: the war on terror, color-coded terror alerts and seemingly endless security lines at airports -- and Sunday offered the chance to shed a portion of that weight.

"We watched the second plane hit the tower, and just watching that was painful," University of Oklahoma senior Steve Sichterman told msnbc's Contessa Brewer. "We were just solemn, and so it is really a great thing to know there is finally justice for those 3,000 plus people that were killed."

“It was really a feeling of relief," said Oklahoma student Timothy Marquis when asked how he reacted to news that bin Laden was dead.

"For ten years we had been searching for him and I remember being in middle school and seeing the attacks on 9/11. Relief came from the feeling that we finally got him," he told Brewer.

At The Ohio State university (user-submitted image below) students plunged into Mirror Lake, a tradition usually saved for the hours surrounding a football game against Michigan.

David Krogh

Students at The Ohio State University jump into Mirror Lake, a tradition marked and remembered during Beat Michigan Week.

Similar scenes were acted out across the country (sans lake, but with the same energy and excitement).

George Washington and American students helped fill the area outside the White House.  

Demi McLaren, 20, a sophomore history and secondary education major at American told the Washington Post "someone put, ‘Party on the White House lawn,’ on Facebook,” then immediately packed into a car with six other students. “We knew it was going to be a rager.”

Boston Common rocked late into the night thanks to the city's many colleges. Penn State looked like it had just won the Rose Bowl (user-submitted image below). From the looks of pictures submitted to msnbc.com, West Virginia University, known for its couch burnings after Mountaineer football games, lost many a living room centerpiece during the course of the evening. 

Robert A. Kolodzieski

At Penn State University. Absolute once in a lifetime experience! USA! Can't believe this has happened after ten years.

'Intense sense of closure'

In addition to pouring outside, college students took to the Internet in heavy numbers in the hours following the announcement pf bin Laden's death. They searched for a semi-private place to vent, support one another and above all, find closure.

University of Delaware celebrations were branded an "intense sense of closure for people who were frightened little kids in '01" on Twitter. 

Of course, there are students who contend that the fun - which, it must be said, took place for many amid the stress of finals - was less meaningful and more effervescent.

Sean Morrow, a senior at Clark University in Massachusetts, told the Associated Press, that it "is kind of surreal to watch people celebrating someone's death."

Morrow contends he understands it because, for him and many others his age, bin Laden was their boogeyman, "the main negative person of our generation."

"That’s why I think we all went out to celebrate what is not only for the victims receiving justice, but for all those men and women overseas that have fought for so long and are going to continue to be fighting the war on terror," he told the news service.

John F. Ryan

Virginia Military Institute celebrates on Sunday.

Despite the overwhelming scenes of glee, millennials' reactions remain mixed, much like older generations that celebrated in similar fashions across the country. The one common thread seems to be that the evening will go down in history a "where were you when moment."

“Without a doubt, just like with September 11th, we’re all going to remember where we were," University of Oklahoma student Sichterman explained.

"We have all the country songs to remember where we were, and we’ll remember where we were on May 1st, 2011.”

Toby Keith, the gauntlet has been thrown.

Click here for more on the reaction across college campuses and in cities: Ohio State; Oklahoma State; Penn State University; Boston; Washington

Click here and here for more images and accounts of spontaneous celebrations from the evening the world learned of Osama bin Laden's death.

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David Friedman / msnbc.com

Steve Archipolo waits for President Obama's motorcade at Ground Zero in New York City on Thursday.

By Miranda Leitsinger, msnbc.com

 “I wouldn’t be anywhere else but here. … I haven’t slept since then, in peace,”  Steve Archipolo said Thursday, as he stood in the crowd gathered outside the World Trade Center memorial site for President Barack Obama’s wreath-laying ceremony.

Archipolo was referring, of course, to the Sept. 11, 2001, terror attacks orchestrated by Osama bin Laden, who was killed Sunday by U.S. forces in his hideout in Pakistan.

That conjured up fresh memories for the 44-year-old Archipolo, who lives just a few hundred yards from the World Trade Center site. On Thursday, he recalled that he was first alerted to the 9/11 attacks by his son,  who saw one of the planes strike a building from a window in their home.

“This is a little closure in my life to remember the victims who died,” said Archipolo, who was carrying a large American flag he borrowed from his church. “(But) the nightmare is still there.

“It’s 10 years, but we’re never going to be at peace. We’re never going to have that feeling where, ‘we’re safe. We’re always going to be on alert. … We know that we can be attacked at any time.”

Still, he said Thursday’s gathering gave him a “good feeling.”

“I’m proud to be here,” he said. “… Our freedom, they can’t take. It’s just nice to see people out here.”

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David Friedman / msnbc.com

Malynda Irby, in yellow, reacts with the crowd on St. Peter's Church steps as President Barack Obama''s motorcade passes by at Ground Zero in New York City on Thursday. "I just really admire him as a leader," said Irby, who is visiting New York on a work trip from Buffalo. "I've never been so proud of any president in my life as I am of him."

David Friedman / msnbc.com

Irby, in yellow, is emotional after seeing President Obama waving and smiling toward her from the passing motorcade. Speaking about this week of Obama's presidency, Irby said,"This is just a high mark so far."

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From the pool report on the wreath-laying ceremony:

Attendance at the wreath-laying ceremony was tightly restricted. Among those attending were New York Gov. Andrew Cuomo, New Jersey Gov. Chris Christie, Mayor Michael Bloomberg and Port Authority Chairman David Samson.  Uniformed officers from the FDNY, NYPD and Port Authority also stood at attention along the pathway to the site of the ceremony, the Survivor Tree. Other elected officials from the New York area and a group of 9/11 families also viewed the ceremony.  

One of the youngest in attendance was 14-year-old Payton Wall.

As is his habit, Obama read some of the letter sent to the president on Monday, including one from Wall. Payton lost her father, Glen James Wall, in the World Trade Center attack and wrote about how she has handled the loss.  

So Obama asked that she be invited to the ceremony.  When White House staff called Payton's mother, she had no idea that Payton had written the president.  Payton, her mother, her sister and her friend (who also lost her father on 9/11) all were in attendance.

The president is now meeting privately with family members of 9-11 victims.

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Out of sight of the crowd gathered outside, President Barack Obama soberly laid a wreath Thursday at New York's Ground Zero and declared, "When we say we will never forget, we mean what we say."

Returning to the site where Osama bin Laden inflicted his greatest damage, the president closed his eyes and clasped his hands at the outdoor memorial where the twin towers of the World Trade Center once dominated the Manhattan skyline. He shook hands with 9/11 family members and others dressed in black at the site where the skyscrapers were brought down by planes commandeered by bin Laden's followers. Nearly 3,000 people were killed. (The Associated Press provided this reporting.)

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As President Barack Obama’s motorcade arrived at Ground Zero, the more than 1,000 people gathered outside screamed, jumped up and down, waved and flashed “V” signs with their fingers.

Obama waved back from behind his limousine’s closed window.

David Friedman / msnbc.com

Carl Cumberbatch, left, and Adam O'Neil on St. Peter's Church steps, waiting to see the president's motorcade arrive at Ground Zero in New York City.

A few people in the crowd held up signs referring to the killing of Osama bin Laden on Sunday by U.S. special operations forces . “Congratulations! America and the world celebrates,” “Mr. President, America thanks you!” read two of them.

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 A crowd of several hundred people gathered outside Ground Zero Thursday in advance of President Barack Obama’s arrival, even though they weren’t going to be able to see the wreath-laying ceremony at the World Trade Center memorial site in memory of 9-11 victims.

The ceremony was taking place near the center of the plot where the Twin Towers once stood, and the view from beyond the police barricades was blocked by cranes and other construction equipment.

But members of the crowd said they felt it was important to be there nonetheless.

Australian Peter Dunstan, 55, a civil servant from Perth, said he and his wife planned their vacation trip across the U.S. long before they knew about the ceremony, but made sure they were there for it after learning that Obama planned to honor the victims.

“One of the reasons we’re here is Australians died in the World Trade Center,” he said.

He described his emotions as “mixed, bittersweet … just the fact that people died unnecessarily.”

Dunstan said the death of al-Qaida leader Osama bin Laden also was on his mind.

“The perpetrator is dead … he can’t do us any more harm. I think it was justice done. He probably ranks up there with Hitler and his ilk. … I hope it puts the demise of al-Qaida a step closer.”

Adam O’Neil, 70, a retired New Yorker, stood on a nearby corner, in front of St. Peter’s Church.

O’Neil, originally from Trinidad, said one of his third cousins died in the subway station beneath the World Trade Center on 9-11.

He said he decided to stand in front of the church so he could offer a prayer for him as Obama was laying the wreath.  He said that he was doing so on behalf of his entire family – 11 brothers and sisters still in Trinidad.

“I think of him all the time,” he said of his cousin, adding that the memory leaves him “very sad.” “This feeling will be with me the rest of my life.”

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David Friedman / msnbc.com

Tyrone and Gayle Stallings took their great-nieces out of school to attend Thursday's wreath-laying ceremony at Ground Zero to commenorate the victims of the Sept. 11 terror attacks.

More than an hour before President Barack Obama was due to arrive at Ground Zero to lay a wreath in memory of the victims of the Sept. 11 terror attacks, several hundred people were gathered outside police barricades in hopes of catching a glimpse of the president.

Among them were Tyrone and Gayle Stallings from Roselle, N.J., who said they took their great-nieces, Brielle Campbell, 6, and Jaylaah Lee, 10, out of school to attend the ceremony at the site of the fallen World Trade Center.

“I thought this was better history than a history class,” Gayle said. She said she hoped the girls would come away with the understanding “that the country is still together …  our spirit is alive.”

She said she delivered the first piece of the lesson as they walked out of the subway, telling the girls that: “The souls of innocent people are in the building. It was full of life. Now we’re just coming through a hole.”

Tyrone said that the death of al-Qaida leader Osama bin Laden on Sunday provided added impetus for the trip, adding, “Today feels good. … It did give some closure at least.”

David Friedman / msnbc.com

A flag seller works the crowd waiting outside the site of the fallen World Trade Center, more than an hour before President Barack Obama's arrival for a wreath-laying ceremony.

But he echoed the words of U.S. counterterrorism officials in warning that the war on terror is not over. “We’re going to have to remain vigilant still ... probably forever,” he said.