The manhunt stretched into a third day, with law officers questioning drivers and searching trunks at checkpoints near the Clinton Correctional Facility in northern New York state, even though authorities said David Sweat and Richard Matt could be anywhere — perhaps Canada or Mexico.
The prison is just over 30 kilometres from the Canadian border.
A spokesman for the RCMP said the force was aware of the matter but had no information to indicate that the two men had crossed the border into Canada.
"The RCMP works closely with government and law enforcement agencies in Canada and the United States and shares information on an ongoing basis to ensure security along the border," said Sgt. Harold Pfleiderer.
A spokesman with the Ontario Provincial Police said its officers had also heard of the escape south of the border through media reports and would always be on the lookout, but were not engaged in any formal efforts related to the incident.
Canada Border Services Agency on the weekend sent a "look out" on the escape to its officers and said Monday it continued to exercise its usual vigilance.
With authorities warning that the men were desperate and dangerous, some residents were nervous over the escape from the 3,000-inmate prison in the middle of the small town of Dannemora, N.Y., close to the Canadian border. But others figured the killers were long gone.
"We always joke about it. We're so close to the prison — that's the last place that anyone who escaped would want to be," Jessica Lashway said as she waited for the bus with her school-age children a few doors down from the hulking, fortress-like prison.
Sweat, 34, and Matt, 48, sliced through a steel wall, crawled down a catwalk, broke through a brick wall, cut their way in and out of a steam pipe and emerged through a manhole to make their escape, discovered early Saturday, authorities said.
They 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, though officials have given no details on how the men managed to avoid detection.
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.
The breakout — which by all accounts took days to pull off — raised a host of other questions that suggested either inside help or a breakdown in security.
"Why did nobody hear it? Officers should have been aware of it if they had done proper cell searches," said Martin Horn, a former New York City correction commissioner and a professor at the John Jay College of Criminal Justice.
Also, how did the inmates hide the hole and the dirt and dust as they cut their way through? And did they have access to blueprints or other inside information to chart their path through the bowels of the prison?
Cuomo said other inmates claimed they didn't see or hear anything. "They're all heavy sleepers," he said sardonically. 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.
A $100,000 reward was posted over the weekend for information leading to the men's capture.
Across the state in Broome County, where Sweat was convicted in the 2002 killing of a sheriff's deputy, authorities warned people involved in the case to stay alert. Sweat was serving a sentence of life without parole.
And the governor noted that Matt had a connection to Mexico: He was convicted of killing a man there while on the lam after being accused of dismembering his Buffalo-area boss in 1997, the crime for which he was serving 25 years to life.
Virtanen reported from Albany, N.Y. Associated Press writers Jennifer Peltz, Jake Pearson and Verena Dobnik in New York contributed to this report.
With files from The Canadian Press
This story has been corrected to show the prison was opened in 1845, not built in 1865, making it 170 years old, not 150.