© Associated Press photo/ file
A naked man who went on a stabbing spree at his Manhattan apartment building, killing an elderly man and injuring four others, was charged with murder on Wednesday, police said.

Christian Falero, 23, was arrested after he randomly knocked on several tenants' doors of the seven-story Washington Heights building and then stabbed the people who answered with a 10-inch kitchen knife, police said.

Police charged him with second-degree murder and robbery.

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; one of the women was in critical condition, 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.