(AP) -- As investigators seek accomplices who may have helped two convicted murderers escape a maximum-security prison, many other questions remain about the brash, elaborate breakout.

How could nobody hear prisoners slicing through a steel wall, breaking through brick and cutting their way in and out of a steam pipe -- or why did those who heard stay silent? How did the inmates hide the hole, the dirt and dust from work that likely took days to accomplish? Did they have access to blueprints or other inside information to chart their path through the bowels of the prison?

And as a manhunt for the missing prisoners stretches into a fourth day, there is a deepening unknown: "what the rest of the plan was," says Rick Mathews, the director of the University at Albany's National Center for Security and Preparedness.

"Where were they going to go, and how were they going to do it?"

As investigators questioned prison workers and outside contractors Monday to try to find out who may have supplied power tools used in the "Shawshank Redemption"-style escape, law officers questioned drivers and searched trunks at checkpoints near the Clinton Correctional Facility in far northern New York. But authorities said David Sweat and Richard Matt could be anywhere -- perhaps Canada or Mexico.

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, 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, ultimately 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 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.

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.

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. Sweet was serving a sentence of life without parole.

The Royal Canadian Mounted Police advised officers to be on the lookout close to the border, 20 miles from the prison.

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.

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Virtanen reported from Albany. Associated Press writers Jennifer Peltz, Jake Pearson and Verena Dobnik in New York contributed to this report.