Laid off from a meter factory in the central city of Hangzhou, Tang, 47, briefly sustained himself as a security guard. Then, two years ago, he found himself idle, broke and living alone in a rented room with no furniture and no future.

Friends and former co-workers said he was irritable, unmoored and unable to find his footing in China's surging economy.

But even though Tang had moments of despair and frustration, those who knew him were at a loss to explain why he attacked a couple of American tourists and their Chinese guide on Saturday, fatally stabbing a 62-year-old man and slashing the others before leaping to his death from the balcony of the Drum Tower, one of Beijing's best-known historic monuments.

Todd Bachman, a Minnesota businessman whose son-in-law coaches the men's volleyball team, was killed. His wife, Barbara, 62, was critically wounded, as was the guide, whose name has not been released.

The attack, on the first day of the Olympic Games, punctured the feel-good bubble that had enveloped Beijing since the opening ceremonies on Friday night. Although the episode received modest coverage in the Chinese media, it has been widely discussed among residents and foreign visitors, many of whom said they were stunned that such an act of brutality could have occurred amid the city's thick blanket of security.

President Hu Jintao, meeting with President Bush on Sunday, expressed condolences to the victims and their families and said the police will investigate. "The Chinese side takes this unfortunate incident very seriously," he said.

The killing has provoked hand-wringing and debate on the Internet. Some people fretted that it could tarnish China's moment of Olympic glory, while others used Tang's murderous outburst to rail against a variety of unattended social ills: mental illness, chronic unemployment among laid-off state workers and the rise of xenophobic nationalism.

One widely circulated posting, written anonymously on a popular Web site, seemed to capture the prevailing worry that Tang's crime will tarnish China's image: "Your actions have hurt not just two Americans, but they have hurt the way Americans will view China during the games, the way all the people of the world will view China. The bright dream of these momentous Olympics has been darkened by you."

Much of the debate and the supposition about his motives have been swirling in a vacuum of substantial information. Tang was unemployed and arrived in Beijing on Aug. 1 for reasons that remain unclear. All he left behind, investigators said, was the government-issued ID card in his pocket.

The Chinese police have painted him as a man turned desperate by personal shortcomings. "He had lost all hope after a series of failures in his life and took his anger out on society," the police said, according to Xinhua, the state news agency.

Tang had no criminal record, investigators said, nor was he among the swarms of aggrieved citizens, so-called petitioners, who flock to the capital to file official appeals to the central government.

On the outskirts of Hangzhou, where Tang spent most of his life, neighbors and former co-workers said he was often disgruntled and prone to argument. "He grumbled a great deal, very cynical," Zhang Liping, a former colleague, said. "He had an unyielding mouth."

Tang worked as a metal presser at the Hangzhou Meter Factory for more than two decades. When a private company bought the plant five or six years ago, his job was transferred elsewhere and Tang was demoted to guard at the factory gate. In 2004, colleagues said, he lost that job for reasons that were not clear.

In 2006, his wife, who also worked at the meter factory, divorced him. Tang sold his house and rented a room nearby in Hengjie, a once-rural town that has become absorbed into Hangzhou's industrial sprawl. Xinhua, quoting the police, said Tang's 21-year-old son spent the money from the sale of the home. Last year the son was arrested for fraud and later received a six-month sentence for burglary.

Jiang Beigen, his landlord, said Tang paid $53 a month for an unfurnished room. According to Jiang and other tenants, Tang seemed to own only one shirt and a single pair of pants, both of which he washed by hand at night. He had no job, they said, and often slept late into the day.

Last week, Tang announced he was leaving town. According to the police, he called his son that evening and told him he would not be returning until he found success.

This article appeared on page A - 12 of the San Francisco Chronicle