The officers ran from the school and Nash spotted the suspect, Sayfullo Saipov, 29, shouting and brandishing what turned out to be a paint-ball gun and a pellet gun.
Nash and another officer were responding to an unrelated call Tuesday afternoon at Stuyvesant High School when they were alerted by civilians about an apparent auto crash nearby, said John Miller, NYPD deputy commissioner.
NY counter terrorism officers claimed Saipov was following ISIL instructions nearly "to a tee".
Nash fired nine shots at Saipov, ending the worst terrorist attack in New York City since September 11, 2001. They showed great courage.
When Saipov dropped to the pavement, a civilian - who had previously attempted to tackle the suspect as he was getting out of the rented truck - approached the wounded man, who was still clutching the two weapons. Police Officer Ryan Nash risked his life to save others. But Nash didn't know that when he confronted the suspect, O'Neill said.
- Sayfullo Saipov sped a rented truck down almost a mile of a Hudson River bike path on Tuesday afternoon, crushing eight people to death and injuring 11 more, before crashing in front of Stuyvesant High School in Tribeca.
"This is what he did for the city, and this is what he did for the country", O'Neill said.More news: NY attack: Trump uses terror to push extreme vetting
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Saipov, an Uzbeki immigrant and part-time Uber driver residing in Paterson, New Jersey, was hospitalized after the attack and remained in critical condition Wednesday.
Mayor Bill de Blasio and other civic leaders commended Nash for his cool head - and said he was a humble officer who felt like he was just doing his job.
"It's the men and women who are out there every day, who are on the first line and I think Officer Nash really showed how important they are and how talented and how fearless". "He thought this was all in a day's work".
Officer Nash has two awards for excellent police duty, one for meritorious police duty from the NYPD and will soon be decorated with more.
Gov. Andrew M. Cuomo joined in the praise, calling the officer "talented" and "brave".
"Here's the hero cop the world should be talking about", City Councilman Joe Borelli tweeted.