Little has been told beyond the Chinese press about the people who died and about Mr. Zhuo, the father left behind, and Mr. Chen, the cousin. He is awaiting a hearing on whether he is mentally competent to stand trial for murder.

Both cousins had come to New York the same way, as young men sent away from home to grind away at busboy and wok-cook jobs that offer only the merest hope of a better life. But Mr. Zhuo built his chance into a humble career, home and family.

What little he had, his cousin — struggling, envious, desperate — is accused of shattering in one night.

Fired from yet another job and on the verge of deportation, Mr. Chen came to stay in the family’s 57th Street apartment in October. He gambled. He smoked. He did not act right, Ms. Li told relatives. Days before the stabbings, Mr. Chen had argued with the children. The night of Oct. 26, Ms. Li, in a call with her mother-in-law in China, told her that Mr. Chen had a knife. By the time concerned relatives came to her door and Mr. Zhuo rushed home from work, it was too late.

Soon after his arrest, Mr. Chen told detectives that “everyone seems to be doing better than him” since he arrived in the United States in 2004, according to the police.

His family, and Mr. Zhuo’s, had borrowed tens of thousands of dollars from relatives and friends for Chinese smuggling rings, known as snakeheads, to sneak their sons into New York City.