Casquejo told police, "I went to the rooftop and climbed the ladder all the way to the antenna," according to the complaint.
WABC-TV reported that he took pictures from the top of the building. Authorities said they were trying to determine his motive. He was arrested in the building by a Port authority police officer, and his camera and cellphone were seized, Pentangelo said.
Investigators said they were working to cement where the teen went within the building and whether he might have skirted anyone else along the way.
The security guard's former employer, The Durst Organization, declined to discuss Sunday's incident or say whether other guards were working, but it said it had reviewed its security at 1 World Trade Center and was working "to improve coordination" with the Port Authority, which owns the site.
Patrick Flores, an 18-year-old neighbor who grew up with Casquejo, described him as "a really good kid" highly interested in adventure.
"He was always the one climbing the cliffs, doing something stupid," Flores said, referring to the cliffs on which Weehawken sits, across the Hudson River from Manhattan, with clear views of the World Trade Center and the rest of the Manhattan skyline. "But that was him — that was his life."
Flores said Casquejo had recently become interested in parkour, the extreme sport that combines elements from martial arts, gymnastics and rock climbing and has become popular thanks to YouTube videos of acrobatic athletes vaulting over obstacles including park benches, trees, guardrails and buildings.
If Casquejo were looking for bragging rights, he could scarcely have picked a more prominent building. Throughout its rebuilding since the Sept. 11, 2001, terrorist attacks, the building once known as the Freedom Tower has been enmeshed in elaborate security plans.
Ultimately, plans call for a $40 million system of barriers and checkpoints around the 16-acre trade center, which includes several towers, the Sept. 11 memorial, a transit hub and other features.