DANNEMORA, N.Y. — State police expanded the search Wednesday for two escaped murderers beyond a 16-square-mile area of woods, fields and swamps where the manhunt has been most intense.

Clinton County Sheriff David Favro said Tuesday that rain in recent days has been washing away any scent dogs might find and interfering with thermal imaging devices used to detect body heat.

No vehicles were reported stolen in the area, which leads searchers to believe convicts David Sweat and Richard Matt were still near the prison they escaped from. Search dogs earlier caught the scent of the men, and authorities found evidence indicating they may have spent time there.

More than 800 law enforcement officers who are combing the rural area now have shifted their focus eastward along Route 374 leading from the village of Dannemora, home of the Clinton Correctional Facility, in far northern New York.

The Clinton County district attorney’s office scheduled a news conference for noon Wednesday in nearby Plattsburgh to provide updates on the search.

Sweat and Matt escaped June 6 from the maximum-security prison near the Canadian border.

Sweat, 35, was serving a life sentence without parole in the killing of a sheriff’s deputy. Matt, 48, was doing 25 years to life for the kidnap, torture and hacksaw dismemberment of his former boss.

Meanwhile, the prison worker charged with helping the killers flee by providing them with hacksaw blades, chisels and other tools had a jail visit Tuesday from her husband, who also works in the prison.

Favro described Joyce Mitchell as “composed” during the morning visit with her husband, Lyle Mitchell.

Prosecutors say Mitchell, a prison tailoring shop instructor who befriended the inmates, had agreed to be the getaway driver but backed out because she still loved her husband and felt guilty for participating.

District Attorney Andrew Wylie said Monday that there was no evidence the men had a Plan B once Mitchell backed out of the escape.

But Favro said while he has “no concrete information,” he doesn’t believe the escapees would have counted only on Mitchell for the success of their “elaborate, well-thought-out escape plan.”

“My theory — my theory only — is that she was Plan B,” he said Tuesday. “I would have viewed her as baggage, almost, for them to be able to escape into freedom because she’s leaving behind a family and a husband.”

He said investigators won’t be certain until the fugitives are caught.

But, Favro said, “I find it difficult to believe right from Day 1 that they would go through that — probably took some time to really map together — and they would get out on the hopes that a civilian worker that they found would assist them in actually getting away.”

Mitchell was charged last week with supplying contraband, including a punch and a screwdriver, to the two inmates. She has pleaded not guilty. She has been suspended without pay from her $57,000-a-year job overseeing inmates who sew clothes and learn to repair sewing machines.

Authorities say the convicts used power tools to cut through the backs of their adjacent cells, broke through a brick wall and then cut into a steam pipe and slithered through it, finally emerging outside the prison walls through a manhole. Wylie says they apparently used tools stored by prison contractors, taking care to return them to their toolboxes after each night’s work.

In Broome County, where Sweat and his cousin killed a deputy in 2002, Sheriff David Harder said his office has been investigating since Sweat broke out of prison, contacting his family and associates and committing about 50 officers to the case. Sweat was “a kind of survivalist,” who was caught in the woods in New York’s Southern Tier five days after that killing after someone came forward with information, he said.

RODRIQUE NGOWI, Associated Press

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Associated Press writer Michael Virtanen in Albany contributed to this report.