Story highlights Justin Casquejo, 16, sneaked past security to the top of 1,776-foot building

He was charged with a count of criminal trespass and one count of trespass

On Twitter, Casquejo posted photos of himself hanging from a crane, standing on a rooftop

A 16-year-old boy from New Jersey was arrested after allegedly trespassing at 1 World Trade Center, bypassing security and making his way to the 104th floor of the nation's tallest building, police said Thursday.

Authorities said Justin Casquejo early Sunday allegedly climbed through a 1-foot opening in a fence surrounding the still-under-construction skyscraper, past "do not enter" and "no trespassing" signs and, apparently undetected, got to the scaffolding around the building and started climbing.

According to the criminal complaint, Casquejo told police, "I walked around the construction site and figured out how to access the Freedom Tower rooftop. I found a way up through the scaffolding, climbed onto the sixth floor, and took the elevator up to the 88th floor. I then took the staircase up to 104th floor."

On the 104th floor, Casquejo encountered an "inattentive" security guard -- a contractor from a security company -- and was able to get past him, according to Joe Pentangelo, a spokesman for the Port Authority of New York and New Jersey, which owns the trade center site. The guard has since been fired, he said.

From there, Casquejo told police, he went to the rooftop and climbed a ladder out to the spire of the 1,776-foot building.

Around 6 a.m. Sunday, Port Authority police arrested Casquejo on the property, according to Pentangelo.

One World Trade Center is rising in the shadows of the original World Trade Center, where the iconic twin towers were felled by two hijacked airplanes on September 11, 2001, in the deadliest terrorist attack on U.S. soil.

The criminal complaint said the teen "knowingly entered and remained unlawfully in a building and upon real property which was fenced and otherwise enclosed in a manner designed to exclude intruders; the defendant knowingly entered and remained unlawfully in and upon premises."

When he was taken into custody, Casquejo had a camera and a phone, Pentangelo said. Warrants have been secured, and the contents of those devices are being checked to establish a motive for Casquejo's alleged trespassing. The investigation continues as authorities review whether Casquejo went anywhere else on the property.

"We take security and these types of infractions very seriously and will prosecute violators," Joe Dunne, chief security officer for the Port Authority, said in a statement. "We continue to reassess our security posture at the site and are constantly working to make this site as secure as possible."

Attempts to reach Casquejo were unsuccessful, but his Twitter page has many photos of himself in various high-altitude locations -- hanging from a crane, standing on a rooftop -- and talks about Parkour, a free-running type exercise that includes obstacle courses, running, climbing and jumping.

According to the Manhattan district attorney's office, Casquejo was released without bail after being arraigned on one count of criminal trespass in the third degree, a misdemeanor punished by up to three months in jail, and one count of trespass, a violation punishable by up to 15 days in jail.

Pamela Griffith, Casquejo's attorney, declined to comment.

One World Trade Center is the United States' tallest building, beating out Chicago's Willis Tower in November.

Upon completion, which is expected this year, the skyscraper is expected to rank as the world's third-tallest building, after the Burj Khalifa in Dubai and the Makkah Royal Clock Tower in Mecca, Saudi Arabia.