A chilling video shows a deranged ex-Marine pumping five shots into an unarmed auxiliary cop slumped behind a car in New York City's Greenwich Village before chasing down the victim's teenage partner and coldbloodedly executing him with a bullet to his head.

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In the shocking footage played by NYPD Commissioner Ray Kelly at a press conference Thursday, it takes gunman David Garvin only seven seconds to kill hero auxiliary cops Nicholas Pekearo, 28, and Eugene Marshalik, 19, on Wednesday night.

Friends said Garvin, 42, a divorced father of two who recently lost his job as a bartender, had become increasingly paranoid. Cops discovered an arsenal of weapons in a bag he dropped near the shooting scene and at his Bronx home.

"You were clearly dealing with a very dangerous individual," Kelly said. "The fact that there were not more lives lost was in no small measure due to the [auxiliary] officers."

Kelly said Garvin had served in the Marines from 1996 to 1998, when he left with a less than honorable discharge. Friends and former colleagues painted a picture of a lonely man who bragged about breaking stories as an award-winning journalist, wrote screenplays and acted in movies.

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