Dozens of officers formed a line and made their way through a pasture and woods in the town of Willsboro while a helicopter hovered above. Other searchers walked nearby railroad tracks.
They descended on the town just west of Lake Champlain after residents reported seeing a couple of men walking on a road late Monday during a driving rainstorm.
The breakout over the weekend from the 3,000-inmate Clinton Correctional Facility in Dannnemora, close to the Canadian border, immediately raised suspicions that the inmates had inside help in cutting through a steel wall, breaking through the bricks and crawling through a steam pipe. They eventually emerged through a manhole outside the prison grounds.
Among the questions: Did someone hear them cutting their way out? How did the inmates hide the hole, the dirt and dust from work that probably took days to accomplish? And did they have access to blueprints or other inside information to chart their path through the bowels of the prison?
Investigators questioned prison workers and outside contractors Monday to try to find out who may have supplied David Sweat and Richard Matt them with the power tools.
Sweat, 34, and Matt, 48, had stuffed their beds with clothes to fool guards making their rounds and left behind a taunting sticky note that read: "Have a nice day."
The prisoners surely had help, and the noise must have been heard, Gov. Andrew Cuomo said.
But Cuomo said other inmates claimed they didn't see or hear anything. "They're all heavy sleepers," he said sardonically. And state Assemblyman Daniel O'Donnell, chairman of the Correction Committee, said any inmate who heard drilling wouldn't dare report it.
"That will get you killed — that's the kind of environment it is," he said.
In looking for those who may have aided the escape, Cuomo said investigators were focusing first on civilian employees and contractors who have been doing extensive renovations at the 170-year-old prison — not on guards.
"I'd be shocked if a correction guard was involved in this, but they definitely had help," the governor said.
Corrections officials said an inventory of the prison's tools has so far shown none missing. But contractors typically come in with truckloads of equipment, said Peter Light, a retired guard who now runs a museum inside the prison.
A $100,000 reward was posted over the weekend for information leading to the men's capture.
The RCMP said Monday it had no information to indicate the two had crossed into Canada.
Sweat was convicted in the 2002 killing of a sheriff's deputy and was doing life without parole. Matt was serving 25 years to life for kidnapping and dismembering his boss in 1997.
Virtanen reported from Albany. Associated Press writers Jennifer Peltz, Jake Pearson and Verena Dobnik in New York City contributed to this report.