NEW YORK (CBSNewYork) — Police are searching for a man who randomly stabbed a woman in the back while she was buying a MetroCard at a subway station on the Upper West Side.

Police released slowed-down surveillance video of a man running a turnstile. The video shows him suddenly lifting up a knife and plunging it downward. Just out of frame, police say a woman buying a MetroCard was stabbed in the back at the West 72nd  Street and Broadway statio.

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Subway riders CBS2’s Natalie Duddridge spoke with were speechless.

“This is horrible. She’s OK now?” said Upper West Side resident Angela Docaj.

The woman will be OK, but authorities say the 40-year-old was treated for a stab wound to her right shoulder at Mount Sinai West Hospital.

The stabbing happened Thursday at noon. Police say the man got off a train and he was carrying some kind of packages in one hand and a large knife in the other.

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The woman told police no words were exchanged between her and the suspect and the attack was totally random.

“I”m always scared of the subway. I’m always trying to be vigilant because you never know,” Docaj said.

Police say the whole incident happened in a flash, and the suspect took off running.

“I think I would try to chase down the guy or at least call police. There are police here all the time at 72nd Street, so I’m surprised that he was even able to get away,” said Upper West Side resident Jerome Noll.

The suspect is described as wearing a blue shirt and bright yellow shorts. He wasn’t wearing a mask, so police have a pretty clear picture of him.

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Anyone with information about him is asked to call the NYPD’s Crime Stoppers hotline at 1-800-577-TIPS (8477), or for Spanish, 1-888-57-PISTA (74782). You can also submit a tip via their website or on Twitter, @NYPDTips. All calls are kept confidential.