AFTER more than two years of bickering with a fellow tenant, Lin Senfeng finally got Yang Jinhua to shut up. At lunchtime on an October day, Mr. Lin burst into the lobby of the Sun Bright Hotel in Chinatown, the building where they lived, covered in blood. Some was his own, oozing from his slit palms. The rest was Mr. Yang's, splattered across Mr. Lin's face. "Call the police!" Mr. Lin screamed. "I don't want him to die!"

When the police arrived, they followed a trail of blood that led up four flights of stairs to find the body of Mr. Yang, dressed in underwear and flip-flops. According to the written confession that Mr. Lin gave the police, he had been depressed about job woes and fed up with Mr. Yang and their spats; he took a four-inch knife that he used for peeling fruit and stabbed Mr. Yang in the neck, arms, face and chest. The medical examiner later determined that Mr. Yang's heart had been slashed.

After the body was found, Mr. Lin, 28, stood somber and silent in the lobby and held out his arms to be handcuffed before he was taken to jail, where he awaits resolution of his case. As the scene unfolded at the hotel, the thoughts of other tenants might have turned to Yee Szegim, another Sun Bright tenant, who had lost his job as a cook and, on a rainy afternoon in April 2004, walked to the Manhattan Bridge and jumped to his death.

All three of these men worked in Chinese restaurants. They and people like them are largely unknown to most New Yorkers; contact typically involves no more than a brisk exchange over a table in a restaurant, or a brief glimpse through an open kitchen door. But occasionally, spasms of violence hint at the bleakness of their world, a bleakness brought on by factors like poverty, language barriers and shadowy immigrant status.