United Flight 116 to Newark, New Jersey, landed safely at Liberty Airport at about 10:40 a.m., and FBI agents met it on the tarmac.
The flight was en route to Newark when a man started acting strangely, passengers said. While the plane was still in the air, the FBI said that the man had claimed everyone aboard was being poisoned, but the agency later said it was working to clarify just what the man said. Passengers said they heard the man claim he himself was going to be poisoned.
"He was afraid of being poisoned. He saw everybody as a threat. He thought everybody was working for the FBI," said passenger Jacques Roizen.
The man even mentioned the name of former National Security Agency contractor Edward Snowden and claimed he, too, had dangerous secrets from the CIA.
In audio recorded by a fellow passenger, the man, who is said to be American, could be heard screaming, "I'm dead. I'm dead already; they're going to kill me! They're going to kill me!"
The man's actions escalated to the point where several passengers had to restrain him. Witnesses say they had to sit on the man to keep him in check.
The United Airlines flight crew made the decision to continue on to Newark. The plane landed without incident as fellow passengers calmed the man down and detained him with plastic handcuffs.
Law enforcement officials say there is no evidence that the passengers were poisoned, and officials believe the man may be emotionally disturbed.
It's not immediately clear if he will face charges or simply receive treatment for a mental illness.
This is far from the first incident of passengers behaving badly on board a plane. On Saturday, a Frontier Airlines plane made an emergency landing after a man on board claimed he was carrying a bomb in a backpack. Also on Saturday, a passenger on an EgyptAir flight from Cairo to New York discovered a sinister note written in pencil inside the restroom. The note reportedly said, "I'll set this plane on fire."
Last month, a man attempted to open an emergency exit door on a plane, but passengers restrained him before he could. In January, a passenger was duct taped to his seat after becoming disruptive. In all of those instances, no one was hurt.
The Associated Press contributed to this report.