Authorities arrested a man in connection with the slashing of a tourist’s face on an Upper West Side sidewalk a day earlier, officials said Thursday.

The 25-year-old young man was detained on 85th Street. Police said the man had previous complaints against him. After his mother saw him on the news, she went to the police station and identified him on Wednesday night.

The FDNY said the attack occurred on Columbus Ave. and Amsterdam Ave. He said it happened just before 10:30 a.m. on West 86th Street between . Surveillance video showed a group of men walking and talking on the sidewalk, and a man in a gray T-shirt and shorts who appeared to be holding a knife in his left hand was seen running behind them.

“It was a completely random incident. The guy came up behind him and cut him,” an unidentified neighbor said. “After cutting this guy, he almost cut off his entire ear.”

The 55-year-old victim is recovering in hospital after having his face, cheek and ear cut, a source told NBC New York. Some good Samaritans at the entrance of an apartment building stepped in to help the victim as he tried to stop the bleeding.

The neighbor said, “He was sitting in the doorway. One of his friends took off his shirt by holding it against his head.” “One of the witnesses was pointing at a man running around the corner.”

It is unknown exactly what led to the stabbing. Just seconds after the man is seen running in the video with the knife, the same man is seen running in the opposite direction while looking over his shoulder.