A second-floor tenant, Ignacio Reyes-Collazo, 81, was killed during the random attacks that unfolded around 4 p.m. Tuesday.
Three women, ages 60 to 85, were stabbed and a 22-year-old home attendant was punched, police said.
They were all taken to area hospitals, where 60-year-old Yanzhi Wang died on Wednesday. The others were stable.
Residents said afterward that the suspect was seen running down the street yelling that it was the end of the world. He underwent a psychiatric evaluation at Harlem Hospital, police said.
His fifth-floor neighbor, Ramon Acosta, 41, said Falero always seemed likable. Acosta came home from work Tuesday to find police outside the building and the suspect's mother in tears.
Acosta said he has known the young man for 10 years and never had a problem with him.
"I guess he just flipped," he said.
Police caught him running down the street naked with the knife.
"He was buck naked," a nearby security guard said. "They handcuffed him. He had blood on his hands. He wasn't making sense."
Neighbors who know the family well speculate that the earthquake upset him.
"I think when he clears up, he's going to be very sorry for what he did," neighbor Bill Adams said.