Shortly after boarding an Orlando-bound plane, passengers say, they saw a man bolt from his seat and run down the aisle, with his screaming wife and man in a Hawaiian shirt behind.

"My husband! My husband!" one passenger said she heard the wife cry.

The chase ended moments later Wednesday in a Miami International Airport jetway, when authorities say Rigoberto Alpizar appeared to reach for his bag. He was shot to death by the man in the Hawaiian shirt and a second pursuer, both undercover air marshals.

Before he ran off the plane he "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 Marshal Service field office in Miami.

No bomb was found, and federal officials later concluded there was no link to terrorism. Witnesses said his wife, Anne, frantically tried to explain he was bipolar, a mental illness also known as manic-depression, and was off his medication.

"She said it was her fault, that he was bipolar," said Mike Beshears, a Flight 924 passenger who works for a vacation club in Orlando. "He was sick and she had convinced him to get on the plane."

It was the first time since the Sept. 11 attacks that an air marshal discharged a firearm at a passenger or suspect, Homeland Security Department spokesman Brian Doyle said.

Dave Adams, a spokesman for the air marshals, confirmed Thursday there were two marshals on the flight and said both fired at Alpizar.

He said the marshals followed proper procedures.

"We only react when there is a threat to the aircraft, passengers or crew," Adams said.

The two marshals joined the force in 2002, he said. One previously worked with the Border Patrol, the other as a Customs inspector. Both have been placed on paid administrative leave while the Miami-Dade Police Department investigates, Adams said.

The Bush administration hired thousands of additional air marshals after Sept. 11, when the nation had only 33. The exact number now is classified. Marshals fly undercover, and which planes they're on is a closely guarded secret.

Officials declined to say how many times Alpizar was shot, but passengers reported hearing between four to six shots. Authorities did not confirm he suffered from a mental illness.

"The man sitting next to me got on the floor," said passenger Olga Echeverria, of Guatemala. "I threw myself on the floor to pray for God's mercy on us."

Alpizar, who worked in the paint department of a home supply store, was returning from a missionary trip, according to a neighbor who was watching his ranch-style house in the Orlando suburb of Maitland. He had arrived in Miami on a flight from Ecuador earlier Wednesday, said Rick Thomas, the airport's federal security director.

"We're all still in shock," said his sister-in-law, Kelley Buechner, in a telephone interview from her home in Milwaukee. "We're just speechless."

Investigators closed the concourse at the airport for half an hour and spread passengers' bags on the tarmac. Dogs sniffed them for explosives, and bomb squad members blew up at least two bags. No bombs were found.

The remaining passengers were kept on the plane for an hour, then police told them to leave with their hands behind their backs, said Lucy Argote, 15, of Codazi, Colombia. They had to leave their possessions behind.

Argote said Alpizar got up from his seat and ran toward the plane's door, with his wife yelling in Spanish.

"Officers told him to stop and he said no," the teen said. "He was running like a crazy man."

Another passenger, Mary Gardner, told WTVJ-TV in Miami that she also heard his wife call after him as he ran down the aisle.

"He was frantic, his arms flailing in the air," she said. She said a woman followed, shouting, "My husband! My husband!"

The Alpizars had been married for about two decades and met when Anne was an exchange student in Costa Rica, family members said. Rigoberto became a naturalized U.S. citizen.

The description of Alpizar by authorities and others stunned his friends and neighbors in central Florida.

"This whole neighborhood is shocked," said Alex McLeod, 16, who lives three houses from the Alpizars. "Totally uncharacteristic of the guy."

Charles Baez, manager of the MAB Paints store in Orlando where Alpizar used to work, described him as a health enthusiast who was always patient with customers.

"He was a quiet, reserved gentleman," Baez said Thursday. "It's very bizarre to me that he would do anything like that."