Three men were found shot dead in a luxury car parked outside New York's Manhattan School of Music and investigators believe it was the result of a drug deal gone bad, police sources said.

The victims, all in their 20s, were discovered at about 6:30pm local time Thursday in a 2012 BMW 750 parked on a leafy Upper West Side street, sources added.

A person leaving Riverside Park saw the three men slumped over and flagged down a police car, sources said.

"It's a very bloody scene," said one source.

The victims were slumped over in the front seats, and the rear passenger side seat.

It is believed the shooter was sitting behind the driver when he unloaded, sources added.

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