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Joyce Mitchell, the prison worker accused of helping two inmates escape in upstate New York, was investigated for a prior sexual incident with escapee David Sweat, sources familiar with the investigation told NBC News.

After the incident, which was investigated by prison officials, the other escapee, Richard Matt, charmed himself into her affection — so much that she "thought it was love," sources said.

District Attorney Andrew Wylie said on Friday that Mitchell was previously investigated because of a complaint that she had a relationship with Sweat, but he said there wasn't "sufficient information" to remove her from the prison or charge her.

In an interview with NBC News, Wylie said Mitchell was going to pick up the two escapees at the prison power plant and run away with them. He said Mitchell brought in blades, drill bits and other tools that helped the prisoners escape.

Mitchell agreed to be the getaway driver but backed out because she still loved her husband, prosecutors said as the manhunt entered its 10th day Monday.

Mitchell agreed to drive Matt and Sweat for up to seven hours over rough terrain but didn’t know where they were headed, District Attorney Andrew Wylie told NBC station WPTZ.

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"Basically, when it was go-time and it was the actual day of the event, I do think she got cold feet and realized, 'What am I doing?'" Wylie told The Associated Press. "Reality struck. She realized that, really, the grass wasn't greener on the other side."

Mitchell, who has been cooperating with investigators, is back due in court Monday morning. She is charged with helping the pair escape from the Clinton Correctional Facility on June 6.

‎NBC News also learned from sources familiar with the investigation that the prisoners left behind a series of post-it notes along their escape route. The notes were similar to the one seen in pictures previously released by authorities.

The 51-year-old prison tailoring shop instructor, who had befriended the inmates, is accused of supplying the pair with hacksaw blades, chisels, a punch and a screwdriver.

More than 800 law enforcement officers from New York state, local and federal agencies were assisting in the search, authorities said Sunday night.

“Investigators will continue to search door to door to remind residents to be vigilant,” New York State Police said in a statement.

Schools in the area will open as usual Monday, but outdoor activities are suspended.

Wylie said there was no evidence the men had a Plan B once Mitchell backed out, and no vehicles have been reported stolen in the area.

That has led searchers to believe the men are still near the maximum-security prison in Dannemora, New York. But Gov. Andrew Cuomo admitted Sunday that, for all anyone knows, the convicts could be in Mexico, where one of the inmates had fled after killing his boss in the late 1990s.

Wylie said the killers apparently cut their way out using tools stored by prison contractors, taking care to return them to their toolboxes after each night's work.

He indicated that Mitchell knew of only certain parts of the plot and provided only some of the tools used to execute the escape.

Sweat, 35, 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.