San Francisco ? The passengers sat stunned as they watched a man walk quickly toward the front of American Airlines Flight 1561 as it was descending toward San Francisco. He was screaming and then began pounding on the cockpit door.

“I kept saying to myself: ‘What’s he doing? Does he have a bomb? Is he armed?'” passenger Angelina Marty said.

Another shocked passenger, Andrew Wai, thought, “Could this be it? Are we going down?”

Within moments Sunday, Rageh Almurisi was tackled. Authorities do not yet have a motive.

While Almurisi, 28, of Vallejo, Calif., has no clear or known ties to terrorism, authorities say, the incident underscored fears that extremists may try to mount attacks to retaliate for the death of al-Qaida leader Osama bin Laden last week.

Federal agents are investigating Almurisi’s background. He was carrying a Yemeni passport and a California identification card, authorities said.

Yemen, a nation at the southern tip of the Arabian peninsula, has been a focus of U.S. officials because one of the most active branches of al-Qaida operates in the remote part of the country.

A cousin of the suspect described him as an educated, easygoing person who had arrived in Northern California a year and a half ago from Yemen in search of better opportunities.

He was unable to find work in Vallejo, a town of 100,000 across the bay from San Francisco hit hard by the real estate bust, and recently moved to New York where his brother lived in search of better luck, said Rageh Almoraissi, 29, of Vallejo.

Almurisi had not told his extended family in California that he was returning to the area, Almoraissi said.

“He’s very laid back, he’s always smiling, he’s always laughing. He’s not an angry person,” Almoraissi said. “Everybody’s worried about him. It’s not typical of him.”

Almoraissi said he could not imagine what may have caused his cousin to act as authorities allege he did on the plane, but said he was certain Almurisi was not a terrorist. He said his cousin did not show an interest in politics and was not intensely religious.

“He might have seriously mistaken the cockpit for the bathroom,” Almoraissi said. “He’s only been on three planes in his whole life.” Almurisi was taking classes in California to learn English but was not happy with his progress, his cousin said.

Almurisi went toward the cockpit door 30 minutes before the flight from Chicago was supposed to land on Sunday night, San Francisco airport police Sgt. Michael Rodriguez said. Almurisi was yelling unintelligibly as he brushed past a flight attendant.

Marty, 35, recalled Monday that she and other passengers on the plane were stunned when they saw Almurisi walking down the aisle. She said a woman in a row across from her who speaks Arabic translated that Almurisi said “God is Great!” in Arabic.

Wai, 27, also remembered on Monday that the wife of one of the men who took Almurisi down later said Almurisi was yelling “Allahu Akbar.”

“There was no question in everybody’s mind that he was going to do something,” Marty said.