Investigators work at the scene where two NYPD officers were shot
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Two New York police officers shot dead

21 December 2014 Last updated at 18:46 GMT

Two New York City police officers have been shot dead in their patrol car by a lone gunman in what appears to be an ambush.

The gunman, Ismaaiyl Brinsley, 28, then killed himself in a nearby subway station.

Earlier, Brinsley had posted messages on Instagram threatening police, and referencing the deaths of the unarmed black men Michael Brown and Eric Garner.

Rajini Vaidyanathan reports from Washington.