Story highlights Police say teen Craigslist buyer pulled a gun and had his arm severed when he was run over by an SUV

Zachary Sam, 17, is charged as an adult with criminal possession of a firearm and robbery

Philipp Pierre, 39, is charged with second-degree attempted murder

New York (CNN) It was supposed to be an ordinary buy-and-sell: a Brooklyn teenager buying sneakers from a seller he encountered on Craigslist.

But the Friday afternoon transaction turned out wildly different -- an alleged armed robbery culminating with the teenage suspect's arm severed after an SUV ran over him, according to New York police.

Police say Zachary Sam, 17, met up with Philipp Pierre, 39, to buy a pair of $200 Air Jordan Retro 8 sneakers.

But once inside Pierre's gray Honda Pilot SUV, Sam allegedly pulled a black revolver, pointed it at the man and demanded the sneakers as well as cash, according to Detective Annette Shelton, a police spokeswoman.

Video surveillance obtained by CNN affiliate WABC shows the teen walking across with the street with what police say was the loot as the SUV drives away.

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