Justin Casquejo, 16, broke into the 104th floor of One World Trade Center, the Port Authority said. View Full Caption John Moore/Getty Images

MANHATTAN — A teenage boy slipped through the fortress-like security at the World Trade Center, sneaked past an "inattentive" guard, hopped an elevator and climbed to the antenna of America's tallest building, officials said.

Justin Casquejo, 16, climbed through a foot-wide gap in the site's exterior wall at Vesey and Church streets before scaling scaffolding that ringed 1 World Trade Center and taking an elevator, stairs and an exterior ladder on his way to the top before he was finally arrested about 6 a.m. Sunday, a PAPD spokesman said.

Casquejo, of New Jersey, may have even duped an elevator operator by donning a hard hat to resemble the other workers at the site, according to the New York Post, which first reported the boy's ascent.

In a stunt that raised serious questions about security at one of the world's biggest terrorist targets, the teen was able to meander around the property for at least an hour before he was caught, according to prosecutors and the Port Authority.

The teen told investigators that he cased the construction site ahead of time and figured out the route for his daring climb.

"I found a way up through the scaffolding, climbed onto the 6th floor, and took the elevator up to the 88th floor. Then I took the staircase up to [the] 104th fl. I went to the rooftop and climbed the ladder all the way to the antenna," Casquejo said, according to his criminal complaint.

The teen had a camera and cellphone when he was arrested. Police have since obtained a warrant to search the electronics, the Port Authority said.

The teen was charged with trespassing and released, prosecutors said. He's due back in court on April 2.

The "inattentive" security guard who the teen slipped past on the 104th floor has since been fired, the PAPD said. Sources said that he worked for the Durst Organization, the real estate giant that counts security of 1 WTC among its duties there.

"We take security and these type of infractions extremely seriously and will prosecute violators," said the Port Authority's chief security officer, Joseph Dunne, said in a statement Thursday.

"We continue to reassess our security posture at the site and are constantly working to make this site as secure as possible," Dunne continued.

The Port Authority said it was still investigating the break-in, a spokesman said.

"We take this incident extremely seriously," Jordan Barowitz, a spokesman for The Durst Organization, said. "We have undertaken a top-to-bottom review of our security at One World Trade Center and are working with the Port Authority PD to improve coordination."

Some security measures for the World Trade Center site are so robust with checkpoints, barriers and other measures that some Downtown residents called it "fortress-like" and said it resembled the Berlin Wall in a recent lawsuit, according to the New York Times.

But the full security measures would only go into effect by 2015, according to city documents.