State highway shut down amid search for escaped killers in New York

(CNN)Authorities shut down a major highway in upstate New York early Thursday as they searched for two convicted killers who escaped from a maximum-security prison six days ago.

"Route 374 is likely to remain closed through the morning," New York State Police said in a statement.

It warned residents to expect an increased police presence as authorities investigate a lead. The highway is in Cadyville, about 5 miles from Dannemora, the town the prison is in.

Saranac Central School District, which is near Dannemora, has canceled classes because of police activity, Superintendent Jonathan Parks said.

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

The pair made a brazen escape using power tools over the weekend from the Clinton Correctional Facility in Dannemora, near the Canadian border. The search for them has involved more than 400 law enforcement officers and a $100,000 reward.

As days go by with no sign of the escapees, authorities have set up 50 digital billboards with their photos and information in New York, New Jersey, Massachusetts and Pennsylvania.

How did they escape?

Authorities discovered the two were missing during a 5:30 a.m. Saturday bed check.

Joyce Mitchell, who worked with the convicts in a prison tailoring shop, may have played a role in the breakout, law enforcement officials said. She has worked at the facility for seven years as an industrial training supervisor.

Investigators say they think Mitchell planned to pick up the inmates after their escape but changed her mind at the last minute, a source familiar with the investigation told CNN.

D'Amico said Mitchell had befriended the men and "may have had some sort of role in assisting them." He did not elaborate or provide additional information.

She has not been arrested or charged in connection with their escape and is cooperating with police, the source said.

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.

Desperate and dangerous

With every passing day, the inmates may be getting desperate, which makes them more dangerous, CNN law enforcement analyst Tom Fuentes said.

They'd have to find food, water and money, while trying to get their hands on weapons or a vehicle. The fact that their alleged designated driver changed her mind may add to their frustration.

"That would put every family in that rural (area) in extreme danger," Fuentes said. "If they're feeling like cornered animals out there, they are going to do something drastic to try to ensure their physical survival and their continued freedom out of that prison."

Without any help like a getaway driver, someone who escapes from Clinton can easily get lost, said Jeff Hall, who teaches at the City University of New York and did his dissertation on northern New York prisons.

"The environment is formidable," said Hall, who grew up near the Dannemora prison. "It's rough terrain, and if you're not familiar with it, it can be deadly."

Expanded search

Before the highway closure, authorities had said Wednesday that they were focusing on New York, Vermont and the Canadian province of Quebec.

"We have information that would suggest that Vermont was discussed as a possible location," New York Gov. Andrew Cuomo said Wednesday.

Under an agreement with Vermont, New York state troopers will be allowed across state lines if needed, officials said.

However, authorities said they had no hard information that the men had left New York state.

The escape

The pair's escape was extraordinarily complex.

Using power tools, they cut through a cell wall that included a steel plate, maneuvered across a catwalk, shimmied down six stories to a tunnel of pipes, followed that tunnel, broke through a double-brick wall, cut into a 24-inch steam pipe, climbed through the steam pipe, cut another hole so they could get out of the pipe and finally surfaced through a manhole.

Aside from the mystery of how they got the necessary power tools, many wonder how they could have used them without detection.

Their time on the run is also remarkable.

Most escapees in New York are captured within 24 hours, according to state data. Of 29 inmates who fled between 2002 and 2013, only one was free for more than two days.

Sweat was serving a life sentence without parole for fatally shooting and then running over Broome County Sheriff's Deputy Kevin Tarsia in 2002.

Matt was convicted in the 27-hour kidnapping of a businessman. When the man didn't comply with his demand for money, Matt killed him.