Wen Hui Ruan, 68, was just a block from his East Village home on Friday night when a man stopped him on East Sixth Street and hurled him against a wall. When Mr. Ruan fell to the ground, the man punched him and began stomping on his head.

A witness called 911 to report the attack, but it was several minutes before anyone came to the aid of Mr. Ruan, a retired garment factory worker who came to United States from China two decades ago to seek a better future for his three daughters.

Security video of the attack, posted online by an East Village blog, showed several passers-by continuing past Mr. Ruan’s crumpled form, before a woman knelt down beside him. A law enforcement official said the video of the episode, posted to YouTube by the blog EV Grieve, “appears to be the same” video as the one that investigators have in their possession.

A police spokesman said on Monday that a 911 caller reported the attack at 8:41 p.m. on Friday and that the police arrived at the scene at 8:45 p.m. Mr. Ruan was taken to Bellevue Hospital Center, where on Saturday he died of injuries from the attack, the police said.