Wylie said there was no evidence the men had a "Plan B" once the getaway driver backed out, and no vehicles have been reported stolen in the area.
That has led searchers to believe the men are still near the Clinton Correctional Facility in Dannemora, where the manhunt was in its ninth day Sunday, with hundreds of law enforcement officers slogging through mosquito-infested woods, fields and swamps close to the Canadian border for Richard Matt and David Sweat.
At the same time, Gov. Andrew Cuomo said "We don't know if they are still in the immediate area or if they are in Mexico by now."
New York State Police spokesman Beau Duffy acknowledged authorities don't know where the fugitives are but "we don't have any evidence that they've left the area."
Wylie said it apparently took a long time for the killers to complete their plan, working methodically between midnight and 5 a.m. over many nights.
"They had access, from what we understand, to other tools left in the facility by contractors under policy and were able to open the toolboxes and use those tools and then put them back so nobody would notice," the prosecutor said.
He also said the men had been scouting out the tunnel system under the prison at night for the best way get out.
The convicts used power tools to cut through the back of their adjacent cells, broke through a brick wall, then cut into a steam pipe and slithered through it, finally emerging outside the prison walls through a manhole, authorities said.
Workers on Sunday welded shut a manhole at the base of a wall on the side of the prison where the two men escaped. They also sealed two other manholes on the street near prison, including the one the convicts climbed out of.
Mitchell, 51, was charged Friday with supplying hacksaw blades, chisels, a punch and a screwdriver. Her lawyer entered a not guilty plea on her behalf, and she is due back in court on charges of promoting prison contraband and criminal facilitation. If convicted, she faces up to eight years in prison.
Wylie said Sunday the two inmates planned to have Mitchell drive them about seven hours away to an unknown destination. The Albany-Times Union quoting a law enforcement source, said the destination was a cabin in an undisclosed location in Vermont.
Cuomo said Sunday that there is “zero tolerance” for any state employee who may have facilitated an escape.
Sweat, who turned 35 on Sunday, was serving a life sentence without parole for killing a sheriff's deputy. Matt, 48, was doing 25 years to life for the 1997 kidnap, torture and hacksaw dismemberment of his former boss. New York has offered a $100,000 reward for information leading to their capture.