NY Prison Escape: Inmates Kept Notes About Escape Plan on Cell Walls, Source Says

— -- The convicted murderers who remain at large kept notes on their cell walls and inside the pipes that they used as their escape route ahead of their break from an upstate New York prison 11 days ago, an official involved in the investigation told ABC News.

The notes may have helped Richard Matt and David Sweat prepare for their escape as they spent months mapping out their escape through steam tunnels, the source said.

The notes had in turn served as a trail of clues for investigators, the source said, though authorities now face the prospect of a dearth of new evidence.

Three officials briefed on the ongoing search in upstate New York told ABC News that the consensus is that the trail has grown cold.

There are currently discussions among senior state and federal officials who are trying to decide what the next steps should be and what, if anything, should be said publicly, sources said.

State officials are trying to determine, according to these sources, when Gov. Andrew Cuomo or another representative of his administration might make a public statement acknowledging that the active all-hands search might have stopped being productive and that a new long-term investigative phase needs to start.

Former prison employee Joyce Mitchell, who has been charged with aiding Matt and Sweat in their escape, is now at Rensselaer County Jail in Troy, N.Y., as investigators try to determine what role she allegedly intended to play in the prisoners' escape. She entered a not-guilty plea to the felony charge of promoting prison contraband and a misdemeanor count of criminal facilitation for allegedly helping the inmates escape from Clinton Correctional Facility in Dannemora, New York, on June 6.

"I don't know if she was plan A, plan B, or plan C," Clinton County Sheriff Dave Favro told ABC News of her alleged intended role as a getaway car driver.

The New York State Police announced today that the dragnet is expanding and shifting to other areas surrounding Dannemora based upon information gathered during the investigation.

Officers from multiple law enforcement agencies have searched over 16 square miles to date and have followed more than 1,200 leads, authorities said.