The incident happened around 4:30 a.m. Tuesday on Madison Avenue in East Harlem.
Police say the 19-year-old victim had just gotten out of a cab when the suspect, a paroled rapist and registered sex offender, grabbed her from behind and threw her down between two parked vehicles on the street.
Demetrius Edwards, 34, then repeatedly slammed her head into ice and snow piled on the ground, according to authorities, and tried to rape her.
A witness, 46-year-old Dale Green, heard her screaming and called 911, giving police a detailed description of the suspect. Green knew something was wrong Tuesday morning on Madison and East 138th, when he saw what he saw and heard what he heard.
"She was saying, 'Oh God, no God no! Don't do this, don't do this'", said Green. "In my head, I'm like, 'Ok, gotta get this person's attention. He doesn't know where I am, or who I am. So I'm like, let me scare him off."
Dale did it, at first by shouting out the window.
"He's looking around, trying to find where the person is coming from," said Green. ('So you were able to spook him from your window?') "Exactly," he said.
But Dale was also able to call 911, then chase the suspect up the block, far enough to know exactly how to describe him to cops, and tell them were to catch him. The suspect tried to run but was stopped by police minutes later.
It turns out the suspect, Edwards, is a Level 3 sex offender who served 10 years for raping a 13-year old girl at gunpoint.
He was sent back to prison twice for parole violations and released fairly recently, in September.
"Just to know that I was able to rescue her, because I had a family member that had been raped before. So I know this is a traumatic experience. It can't be a good thing," said Green.
Dale says he knows the victim from the neighborhood. "I wouldn't consider myself a hero. I'm one person here, trying to make a difference," he said.
In this case, a real difference for cops, and the victim of a violent crime.
The victim was taken to Harlem Hospital, where she was treated and released.