NEW YORK – In an era when airline passengers can’t get past a checkpoint with a bottle of shampoo, security experts were shocked Monday by the case of a man who swam ashore, scaled a fence and walked dripping wet into Kennedy Airport despite a $100 million system of surveillance cameras and motion detectors.

“Thank God it wasn’t a terrorist, but we have to look at it as if we had another attack,” said Isaac Yeffet, former chief of security for Israeli airline El Al. “That’s the only way we’ll improve the system.”

The Port Authority of New York and New Jersey, which oversees JFK, quickly added police patrols to the airport perimeter and said it is investigating the security breach.

Authorities said the trouble began Friday evening when Daniel Casillo’s Jet Ski ran out of fuel in Jamaica Bay. Casillo swam toward the lights of Kennedy’s runway 4L, which juts out into the bay, then climbed an 8-foot fence that is part of the airport’s state-of-the-art Perimeter Intrusion Detection System, authorities said.

Soaking wet and wearing a bright-yellow life jacket, Casillo made his way across two intersecting runways — an estimated distance of nearly two miles — before he was spotted on a terminal ramp by an airline employee, authorities said.

According to the police report, Casillo, 31, told an officer: “I needed help!”

The intrusion-detection system, manufactured by defense contractor Raytheon Co., should have set off a series of warnings, said Bobby Egbert, spokesman for the Port Authority police officers union.

“This system is made specifically for those types of threats — water-borne threats,” Egbert said. “It did not detect him climbing over a fence. It did not detect him crossing two active runways.”

Port Authority police interrogated Casillo and charged him with criminal trespassing. Authorities said the airport grounds were clearly marked with no-trespassing signs that indicate it is a “restricted area for authorized personnel only.”

Casillo was released without bail for a court appearance Oct. 2. A man who answered the phone at the home of Casillo’s girlfriend said the couple’s lawyer had advised them to stop speaking to the media.

The Port Authority offered no explanation of what went wrong or whether it was human error or equipment failure. A spokesman for Raytheon would not comment.

“The catastrophic failure was that nobody sounded the alarm to go to condition-red intruder alert,” said former New York City Detective Nicholas Casale, who was deputy director of security for counterterrorism at the New York metropolitan area’s transit agency.

“Immediately there should’ve been an armed response. Heavy weapons, armored cars to the area that the perimeter was breached. The airport should have been locked down.”

The intrusion-detection system employs sensors, motion detectors and video surveillance, Egbert said. A security guard employed by a private contractor is supposed to keep an eye on the footage from a monitoring room.