“Now, every time we leave an elevator and the subway, we feel we have to look over our shoulder to make sure no one is around,” a 35-year-old mother said in Mandarin. She declined to give her name out of concern for her safety.

The Police Department made a priority of ending the robberies. It posted squad cars on corners with flashing lights and sent Chinese-speaking officers like Sgt. Hao Li to walk a beat uptown.

Sergeant Li, who normally oversees officers in Chinatown’s Fifth Precinct, was among those deployed to East Harlem. The sergeant, who, like many new Chinese residents of the city, speaks Fujianese and Mandarin but not Cantonese, said he had not known people were moving up there. “But I was kind of expecting it,” he said. “Chinatown is really too small.”

The police identified Jason Commisso, 34, as the suspect. They said he had once lived in the area. He was arrested in New Jersey on a Greyhound bus; the police said he was seeking to flee to Texas. Mr. Commisso, who is being held on $75,000 bail, has not yet entered a plea; his next scheduled court date is March 14.

Paul J. Browne, the Police Department’s chief spokesman, said the police had occasionally encountered criminal patterns that focused on new immigrants “because of the belief that they may be less likely to call the police, and when they do, they are not as good a witness as somebody who is a native English speaker.”

Many new residents have come to East Harlem through the New York City Housing Authority, which has more than 15,000 public housing units in the neighborhood. The authority has registered a 68 percent rise in Asian residents in the area’s public housing over the past five years, compared with a 33 percent increase in public housing citywide.