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A chunk of airplane debris found near the World Trade Center site that is believed to have come from one of the jetliners hijacked in the 9/11 attacks 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 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 answered that question. The official told 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.

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 an alley only about 18 inches wide between the rear of 50 Murray St. and the back of 51 Park Place, the site where a mosque and community center have been proposed three blocks from ground zero.

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

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."

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

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.