NEW YORK (CBSNewYork) — Illegal dirt bikes sped off with police close behind them on Staten Island this week, and when it was all over, one of the suspects was left fighting for his life.

As CBS2’s Brian Conybeare reported Friday night, exclusive video showed the illegal dirt bikes speeding down South Avenue in the Mariners Harbor section of Staten Island Thursday evening.

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An unmarked NYPD squad car was trailing them.

“I see three guys coming down here, and the cops were chasing them on the dirt bikes,” said witness Nate Dean.

When asked how fast they were all going, Dean said, “I’d say about maybe 40 miles an hour, 50.”

The bikers and police officers all blew through the stop sign at Richmond Terrace, and one biker even veered onto the sidewalk.

Surveillance video picked up what happened next. The third biker on the wrong side of the road slammed into a white pickup truck outside A&J Auto Parts.

Twenty seconds later, a plainclothes officer pulled up in the unmarked car.

“It was a hideous situation,” said Jim Taylor of A&J Auto Parts. “He was locked under the rear axle of the truck.”

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Firefighters and EMTs rushed in to help the seriously injured biker, identified as Walter Aviles, 28.

“You don’t run from the police,” Taylor said. “if you’re doing something wrong, you stop.”

The city is cracking down on illegal dirt bikes and all-terrain vehicles. The NYPD even publicly crushed some of the nearly 700 confiscated this year.

They often use helicopters to avoid dangerous high-speed pursuits.

The NYPD maintained that the officers on Staten Island were only “following and monitoring” the bikers, and not chasing them, which is against department guidelines.

Mayor Bill de Blasio addressed the issue in a radio interview Friday.

“We will not allow – and this is Police Department rules, a prolonged chase, because that creates in some ways even greater safety dangers,” de Blasio said on “The Brian Lehrer Show” on WNYC.

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NYPD officials said they will review the video. Meanwhile, Aviles is charged with reckless endangerment, driving without a license and other offenses. He is expected to survive.