MIAMI – An agitated passenger who claimed to have a bomb in his backpack was shot and killed by a federal air marshal yesterday after he bolted frantically from a jetliner that was boarding for takeoff, officials said. No bomb was found.

It was the first time since the September 11, 2001, attacks that an air marshal had shot at anyone, a Homeland Security Department spokesman, Brian Doyle, said. Another federal official said there was no apparent link to terrorism.

The passenger, identified as Rigoberto Alpizar,a 44-year-old American citizen, was gunned down on a jetway just before the American Airlines plane was about to leave for Orlando, near his home in Maitland.

According to a witness, the man frantically ran down the aisle of the Boeing 757, flailing his arms, while his wife tried to explain that he was mentally ill and had not taken his medication.

The passenger indicated there was a bomb in his bag and was confronted by air marshals but ran off the aircraft, Mr. Doyle said. The marshals went after him and ordered him to get down on the ground, but he did not comply and was shot when he apparently reached into the bag, Mr. Doyle said.

Flight 924, which originated in Quito, Ecuador, had arrived in Miami just after noon, and the shooting occurred shortly after 2 p.m. as the plane was about to take off for Orlando with the man and 119 other passengers and crew, an American Airlines spokesman, Tim Wagner, said. Alpizar had arrived in Miami earlier in the day from Ecuador, authorities said.

After the shooting, investigators spread passengers’ bags on the tarmac and let dogs sniff them for explosives, and bomb squad members blew up at least two bags.

No bomb was found, the agent in charge of the Federal Air Marshals field office in Miami, James Bauer, said. He said there was no reason to believe there was any connection to terrorists.

The concourse where the shooting took place was shut down for a half-hour, but the rest of the airport continued operating, officials said.

“This was an isolated incident,” the airline said in a news release, adding that none of the other passengers or crew members were ever in danger.

Federal officials declined to say how many times Alpizar was shot, or reveal how many air marshals were on the plane.

Mary Gardner, a passenger aboard the Orlando-bound flight, told WTVJTV in Miami that the man ran down the aisle from the rear of the plane. “He was frantic, his arms flailing in the air,” she said. She said a woman followed, shouting, “My husband! My husband!”

Ms. Gardner said she heard the woman say her husband was bipolar – a mental illness also known as manic depression – and had not had his medication.

Ms. Gardner said four to five shots were fired. She could not see the shooting.

After the shooting, police boarded the plane and told the passengers to put their hands on their heads, Ms. Gardner said.

“It was quite scary,” she told the TV station via a cell phone.”They wouldn’t let you move.They wouldn’t let you get anything out of your bag.”

Relatives said Alpizar had been on a working vacation in Peru. “We’re all still in shock. We’re just speechless,” Kelley Beuchner, a sister-in-law, said.

There were only 32 air marshals at the time of the September 11 attacks. The Bush administration hired thousands more afterward, but the exact number is classified.

[The incident was reminiscent of the shooting of Jean Charles de Menezes in London last July. Brazilian-born Menezes was mistakenly taken for a suicide bomber and was shot dead by police officers as he boarded an underground station in South London. The police officers were on high alert due to a suicide bomber attack in London two weeks prior and a failed attack the previous day.]