(NBC NEWS) -- A 5-foot-long chunk of airplane debris found near the World Trade Center site is believed to be a piece of landing gear from one of the planes that hit the towers more than 11 years ago, NBC 4 New York first reported.
Police confirmed Friday that 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, as seen in an exclusive photo obtained by NBC 4 New York. The bent metal chunk contains cables and levers and is about 17 inches wide and 4 feet long, according to The Associated Press.
Police Commissioner Ray Kelly visited the alley Friday evening and viewed the debris from about 30 feet away.
"It's a manifestation of a horrific terrorist act a block and a half away from where we stand," he said. "It brings back terrible memories to anyone who was here or who was involved in that event, and obviously I think the families could very well be impacted by this finding."
Kelly described the piece as being about 5 feet by 4 feet by 17 inches, lying in a "very, very narrow, confined area."
"It's difficult to get in there and see," he said.
He said there was rope intertwined in part of the gear, and there were no marks on the buildings indicating the piece hit the walls on the way down.
"It would have had to fall down at a certain angle," said Kelly.
Asked whether he was surprised to see such a large plane part anchored in such a tight area, Kelly said: "If you see how confined this space is, and you realize the chaos that existed down here on this street, it's not surprising. It's very, very confined. No cleanup went on in this 18-inch space between these two buildings."
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. See below for a map.
Police spokesman Paul Browne said the NYPD has secured the location "as it would a crime scene," and investigators are photographing the scene and restricting access until the medical examiner completes a health and safety evaluation.
Officials said the soil below the piece of debris could also be searched for remains.
Police officials say the part could be difficult to remove, and may require demolition work that would destroy the two surrounding buildings. Officials are expected to be back at the scene on Monday to see if it can be removed.
"It really is a historical artifact," Kelly said.
When plans for the Islamic center at 51 Park Place were made public in 2010, opponents said they didn't want a mosque so close to where Islamic extremists attacked. They argued the site was "sacred" because landing gear from one of the hijacked Boeing 767 jets had punctured the roof of the building on Sept. 11.
During street protests, they clashed with supporters of the center, who said it would promote harmony between Muslims and followers of other faiths.
The building includes a Muslim prayer space that has been open for three years. After protests died down, the center, called Park51, hosted its first exhibit last year. The space remains under renovation.
Mohammed Fekonus, who prays inside the mosque at Park51 and whose son was a Stuyvesant High School student who ran from the dust cloud on Sept. 11, is convinced discoveries like the plane part could be endless.
"We were all emotionally distressed by that event," he said.
"If you really want to look for things, we'll find things 100 years from now."
Donna Marsh O'Connor, who lost her daughter Vanessa Lang Langer in the attacks and is a member of September 11th Families for a Peaceful Tomorrow, called the landing gear discovery "bizarre."
O'Connor is a supporter of the Islamic center and said the fact that the plane fragment was found there "makes me think that this was the right place for a center that was going to heal the divide."
In a statement, Sharif El-Gamal, the president of Soho Properties, which owns 51 Park Place, said workers called the city and the police as soon as they discovered the landing gear. He said the company is cooperating with the city and the police to make sure the piece of equipment "is removed with care as quickly and effectively as possible."
Patricia Riley, whose sister Lorraine Riley was killed in the Sept. 11 attacks, called the landing gear discovery "very strange."
"Twelve years later we are still finding remnants of the attack on our country," she said. "... For years to come we'll continue to find things that we didn't see before. Hopefully, they'll serve as a reminder that we have to stay vigilant."
The Park51 space, a former Burlington Coat factory, is a five-story, mildly run-down building. Renovations are expected to take years and would add an auditorium, a pool, a restaurant and culinary school, a child care facility and artist studios.
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.
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.
Boeing declined comment.