Miami ? An agitated passenger who claimed to have a bomb in his backpack was shot and killed by a federal air marshal Wednesday 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 Sept. 11 attacaks that an air marshal had shot at anyone, Homeland Security Department spokesman Brian Doyle said. Another federal official said there was no apparent link to terrorism.

According to a witness, the passenger 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, identified as Rigoberto Alpizar, “uttered threatening words that included a sentence to the effect that he had a bomb,” said James E. Bauer, agent in charge of the Federal Air Marshals field office in Miami. He was confronted by air marshals but ran off the aircraft. 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.

Alpizar, a 44-year-old U.S. citizen, was gunned down on a jetway outside the American Airlines plane, which was parked at a gate at Miami International Airport. Alpizar had arrived earlier in the day from Quito, Ecuador, and Flight 924 was going to Orlando, near his home in Maitland.

Authorities surround an American Airlines jet at Miami International Airport. A passenger who claimed to have a bomb in a carry-on bag was shot by a federal air marshal Wednesday on a jetway connected to the plane, officials said.

Relatives said Alpizar and his wife had been on a working vacation in Peru. A neighbor who said he had been asked to watch the couple’s home described the vacation as a missionary trip.

“We’re all still in shock. We’re just speechless,” a sister-in-law, Kelley Buechner, said by telephone from her home in Milwaukee.

The shooting occurred shortly after 2 p.m. as Flight 924 was about to take off for Orlando with the man and 119 other passengers and crew, American spokesman Tim Wagner 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, 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.

Federal officials strongly defended Wednesday’s shooting, saying the man presented a serious threat.

“Their training showed they made the right decision, though there turned out to be no bomb in the bag,” said Brian Doyle, a spokesman for the Department of Homeland Security, which includes the air marshals service. “They had a split second to make that decision.”

James E. Bauer, special agent in charge of the air marshals’ Miami field office, said the marshals’ reaction to the perceived threat was by the book.

“They were justified in their shooting because of the threat posed by this man,” Bauer said.

The U.S. government has hired two Miami lawyers to represent the two air marshals during the shooting inquiry, a standard procedure in such cases.