Highway, schools closed amid search for escaped killers in New York

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(CNN) -- Law enforcement swarmed around a swath of upstate New York on Thursday morning, focused on finding convicted murderers-turned-prison escapees Richard Matt and David Sweat.

There have been no confirmed sightings of either man since Clinton Correctional Facility guards found their cells empty during a 5:30 a.m. Saturday bed check. Nor have there been publicized reports of break-ins, car thefts or other actions that might indicate where Matt and Sweat have been, what they have or where they're going.

However, there have been leads, and the latest centers on an area a few miles east of the maximum-security prison in Dannemora.

While not elaborating, New York State Police spokesman William Duffy said this latest tip came in "last night." Almost immediately after it did, authorities shut down several miles of State Route 374, setting up checkpoints and sending swarms of law enforcement officers to the area.

The heavy law enforcement presence and prospect of killers on the loose prompted the cancellation of classes Thursday in the Saranac Central School District, which includes Dannemora.

"They are going to be searching that area," Duffy said Thursday morning of the stretch of Route 374. "(It) will be closed down until further notice."

Lake and campsites searched in Vermont

While the focus appears to be in Dannemora and nearby Cadyville, those aren't the only places authorities are looking.

Hundreds of officers have scoured neighboring woods, looking "behind every tree, under every rock and inside every structure" for Matt, 48, and Sweat, 34, New York State Police Superintendent Joseph D'Amico said.

Earlier this week, they searched farms, fields and woods in Willsboro after a driver saw two "suspicious" men run off during a late-night driving rainstorm. Then there was a turn toward Vermont because of "information that would suggest (that state) was discussed as a possible location," New York Gov. Andrew Cuomo said Wednesday. Vermont state police vessels and troopers looked for the fugitives on Lake Champlain, which straddles the two states, as well as in nearby campsites.

That said, authorities don't have any hard information that Matt and Sweat have left New York. Nor can they discount the possibility they have left the area, perhaps heading to Canada -- which is just 20 miles north of the prison -- or most anywhere in the United States or beyond. To this point, 50 digital billboards with the fugitives' photos have gone up in New York, New Jersey, Massachusetts and Pennsylvania.

"(Authorities) are not just staying local," Lenny DePaul, a former regional task force commander for the U.S. Marshals Service, told CNN on Thursday. "(People should) not think that they're cornered somewhere in New York. So they have to keep their eyes open and be vigilant."

Remarkable escape, time on the lam

In many sinister ways, Matt and Sweat have already proved themselves remarkable.

First, there was what landed them in jail. Matt held a businessman hostage for 27 hours, and then tortured and killed him after he wouldn't give him more money. Sweat was serving a life sentence without parole for fatally shooting and then running over Broome County Sheriff's Deputy Kevin Tarsia.

Then, there's how they escaped -- using power tools to get out of their cells and cut into a steam pipe, navigating a tunnel of pipes and finally surfacing out a manhole.

And lastly, there's the matter of how they've remained on the loose for so long. Authorities have been looking them for six days now. To put that in perspective, state data indicates most escapees in New York are captured within 24 hours. Of 29 inmates who fled between 2002 and 2013, only one was free for more than two days.

Prison worker 'may have' helped escapees

How have they done it?

With help, many suspect.

D'Amico said Joyce Mitchell, an industrial training supervisor the past seven years at the prison who worked with the convicts in a tailoring shop, had befriended the men and "may have had some sort of role in assisting them."

The state police superintendent did not elaborate. But according to a source close to the investigation, authorities believe Mitchell planned to pick up the inmates after their escape but changed her mind at the last minute. Her cell phone was used to call several people connected to Matt, according to another source. It's unclear who made the calls, when they were made or whether Mitchell knew about them.

Mitchell is cooperating with police and has not been arrested or charged, one of the sources said. And her family is standing behind her, with her daughter-in-law telling CNN that "95% of what is being said" is not true.

Paige Mitchell denied that her mother-in-law was to be the getaway driver and that she helped provide power tools used in the escape. She added that Matt may have persuaded her mother-in-law to contact people for him who knew about art, saying, "Her heart was in the right place."

"They don't have the facts to prove this," she said of Joyce Mitchell's alleged involvement. "This is just slander and rumor."