Dec. 7 (Bloomberg) -- A U.S. air marshal shot and killed a 44- year-old U.S. citizen on a jetway linking American Airlines Flight 924 to the airport terminal in Miami, after the passenger said a carry-on bag contained a bomb. No bomb was found.

It was the first time an air marshal has fired a gun on duty since more armed officers were deployed on airliners after the Sept. 11, 2001 terrorist attacks, said Brian Doyle, a Homeland Security Department spokesman. Federal marshals confronted the passenger on the plane, which stopped at Miami International Airport en route from Medellin, Colombia, to Orlando, Doyle said.

The backpack-carrying passenger, Rigoberto Alpizar, claimed to have a bomb, said James Bauer, special agent in charge of the Federal Air Marshals Service's Miami field office. Alpizar, who left through the passageway at gate D-42, was ordered to get down, Doyle said. He appeared to be reaching into a bag and a marshal fired at him, Doyle said.

Alpizar's wife tried to explain he was mentally ill when the incident happened and that he had not taken his medication, Associated Press reported, citing witnesses on the aircraft.

``There were no explosives on the plane,'' Bauer said during a press conference. ``There's no reason to believe there's a nexus to terrorism.''

Alpizar had arrived earlier from Quito, Ecuador, cleared customs and boarded a flight to Orlando, said Rick Thomas of the Transportation Security Administration at the Miami airport.

Increasing Marshals

The plane, a Boeing 757, and passengers are still in Miami, said Lisa Bailey, an American spokeswoman. The incident isn't affecting other American flights into or out of Miami, she said. American Airlines is owned by AMR Corp., based in Fort Worth, Texas.

``None of the other 113 passengers on board were affected or in any danger,'' said Tim Smith, a spokesman for AMR.

Marshals, who dress in plain clothes and carry firearms, work in teams aboard flights. The marshals fly on a portion of the 27,400 daily U.S. and international flights.

Congress increased the number of air marshals to thousands from just 33 after the Sept. 11, 2001, terrorist hijackings. U.S. officials don't disclose the number of marshals aboard the flights to disrupt terrorist planning, according to the Federal Air Marshal Service Web site.

Miami International handled 30.2 million passengers in 2004, or about 89,000 a day during the week, making the airport No. 15 in the U.S., according to the Miami-Dade Aviation Department. Of those passengers, the D concourse had 2,961,525 people, according to the department.

Screening Passengers

Responsibility for screening passengers and luggage before flights leave Medellin rests with the Colombian government and the airlines, said Zachary Mann, special agent and spokesman for U.S. Customs and Border Protection.

The agency's ``mission is really to process, examine, detect and inspect all persons and commodities entering the United States,'' Mann said in an interview today.

American, the world's largest airline, said Miami-Dade police and Federal Air Marshal Service had jurisdiction in the matter. If a crime has been committed aboard the plane or there is a terrorism link, the Federal Bureau of Investigation would head the investigation, Bauer said in the briefing.

``The airline is secure, the bags are secure and there really is no bomb,'' said Bobby Parker, director of the Miami-Dade Police Department, in the briefing today.

To contact the reporter on this story: Theresa Barry in Washington at tbarry2@bloomberg.net

Last Updated: December 7, 2005 23:27 EST