Richard Matt, 49, was killed yesterday in the upstate town of Malone, less than 16 kilometers from the Canada border, New York state police said.
Officers were still hunting for 35-year-old David Sweat, Matt's accomplice in the spectacular, Hollywood-style prison break from Clinton Correctional Facility on June 6, about 40 miles from Malone.
"A member of law enforcement shot and killed a man believed to be Clinton Correctional Facility escapee Richard Matt," New York state police said.
One of New York's two senators, Democrat Chuck Schumer, told the local CBS affiliate that Matt had been shot and killed by a federal border patrol agent.
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The inmates used power tools to cut their way out of their prison cells before dawn on June 6, triggering an intense weeks-long manhunt in the state.
The audacious escape sparked a huge search involving more than 1,100 personnel backed by sniffer dogs and helicopters to find the men, who had been spotted in several locations in recent days in upstate New York.
Reports emerged that a shotgun is missing from a remote cabin where DNA traces and a bloodied sock indicate the men were most likely holed up.
Two prison workers have been charged over the brazen breakout, and are accused of smuggling tools and contraband items to the pair in hamburger meat.
Matt and Sweat used power tools to cut through cell walls and crawled through pipes to emerge from a manhole in the village of Dannemora, home to the sprawling prison.
Matt, six feet (1.83 meters) tall with multiple tattoos, was serving a sentence of 25 years to life for the 1997 kidnapping and dismembering of his former boss in a 27-hour ordeal.
Sweat was serving a life sentence without parole for murdering a sheriff's deputy in New York state in 2002 when he was 22.