A New York City subway slashing victim can be heard screaming for help and pursuing her own attacker as other riders appear to do nothing, the footage shows.

"Somebody call 911! Somebody call 911!" the 28-year-old woman can be heard wailing. "Pull the emergency brake!" 

The seriously injured straphanger, her leg dripping with blood, pursued the slasher through the door connecting two subway cars and captured video of him casually walking away, according to the cellphone footage obtained exclusively by the New York Post.

About a dozen riders can be seen gawking at the woman as she enters the car, but appear to offer no help. The Sunday afternoon subway attack was the third in 20 minutes by the same perpetrator, the local newspaper reported.

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Serial slasher Kemal Rideout was arrested for the vicious assaults.

Kemal Rideout, left, is accused of slashing three women in the course of 20 minutes on the New York City subway Sunday. One victim, right, shows her injured leg.  (NYPD/New York Post)

The woman, whose name was withheld, was slashed on the southbound No. 4 train at 4:30 p.m. as the car neared the Brooklyn Bridge-City Hall station.

"I was on the train, texting my boyfriend," she told ABC7-News. "Some random guy walked past me and sliced me — I don’t know what he used — and nonchalantly walked away. My body was in shock. I didn’t feel the pain right away."

Despite the gaping gash in her leg, the woman's first instinct was to get a video of her attacker, she said.

Police on Tuesday arrested Kemal Rideout, 28, on three counts of felony assault for allegedly slashing three women Sunday – including the 28-year-old who shot the video that helped authorities identify him.

A dozen blanked face riders gawk at an injured woman after she was slashed.

New York City subway riders stare at a woman as she stumbles into a car with a slashed leg to pursue her attacker, who is about to exit the car at the far end of the image. (New York Post)

"She is a hero," the woman's mother told The Post on Wednesday after Rideout appeared in court and was ordered held without bail. "She picked herself up. She did good. She got up and dragged herself through the train with her wounds and got a shot of him."

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The victim, who was the most seriously injured of the three women, required a tourniquet to close the gash before she was rushed to Bellevue Hospital. Horrifying photos show a cut that appears to reveal the bone.

The trauma has left a permanent mark.

A deep, bleeding wound on a leg.

Close-up of gash on the leg of a New York City subway rider who was one of three women slashed in a random attack.

"Her mental state will never be the same," her mother said. "She will always be looking behind her back. I need her to see a therapist. Her mental state is not good. She has to speak about it."

Rideout allegedly first slashed Bianchelli Diplan, 19, at 4:15 p.m. at the 86th Street and Lexington Avenue station on the Upper East Side as she walked up the stairs. 

"I didn’t know he was behind me on the stairs," Diplan said. "I felt the cut. It felt like somebody cut me deeply. I looked back at him, and he just stared at me, then walked away. I just started crying."

Slashing suspect wears Boston Red Sox hat and white Graphic T standing at NYC subway turnstile

The who is accused of slashing three women in the legs within the New York City subway system Sunday. (NYPD)

She needed 19 stitches. Rideout allegedly cut a second woman with what appeared to be a piece of glass, and she required 48 stitches.

The serial slasher was arrested after he was kicked off a city bus for not paying the fare, and police recognized that he was wearing the same shoes as the man in the slashing videos, according to court papers.

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Rideout has five priors in New York, including for attempted rape, assault, criminal mischief and forcible touching, the Post reported.