DANNEMORA, N.Y. – Authorities questioned inmates at New York’s largest maximum security prison Sunday in an effort to solve the mystery of how two killers executed the first escape ever from the 150-year-old facility.

Gov. Andrew Cuomo said he talked with prisoners in the cellblock that housed the escapees, chiding the inmates as heavy sleepers for not alerting officials to the breakout plot reminiscent of the movie “Shawshank Redemption.”

“They were heard,” said Cuomo, referring to power tools used in the escape from the Clinton Correctional Facility 20 miles from the Canadian border. “They had to be heard.”

Richard Matt, 48, and David Sweat, 34, were discovered missing from their adjoining cells at 5:30 a.m. Saturday when they failed to respond to a morning bed call. More than 200 law officers, aided by helicopters and bloodhounds, searched the rugged terrain of New York’s northeast corner for them.

The convicts faked out nighttime guards who made walk-by checks every two hours by placing dummies of crumpled clothes and hooded sweatshirts beneath their bed blankets. The escapees were last seen by guards at 10:30 p.m. Friday.

Prison officials said they used power tools to cut holes in the thick cell walls behind their beds, climbed onto a six-foot-long catwalk and shimmed down and through a maze of steam pipes to the bowels of the prison, where they cut a hole in a sewer outflow tunnel.

They emerged through a manhole cover outside the prison’s 30-foot concrete walls, leaving behind a yellow sticker note on the cut tunnel saying, “Have A Nice Day” and a containing a drawing of a bucktoothed caricature.

Cuomo said it is not known where or how the killers obtained the power tools needed for the escape. He said all prison tools were accounted for and that officials were checking with outside contractors working on projects at the prison.

“We went back and pieced together what they did,” said Cuomo. “It was elaborate. It was sophisticated. It encompassed drilling through steel walls and pipes and so this was not easily accomplished. We want to find out exactly how it happened. How did they get the power tools? From who? How?”

Anthony Annuci, acting state corrections commissioner, said officials were surprised the escapees knew so much about the prison’s hidden infrastructure of pipes and tunnels.

“It may have been over a period of time,” he said. “It may have been trial and error. We don’t know.”

Sweat, the younger of the two escapees, was serving a life without parole for the 2002 first-degree murder of a sheriff’s deputy. Matt was serving 25 years to life for the kidnapping and second-degree murder of his former boss in the Buffalo area in 1997.

Authorities searched door-to-door in the tiny community of Dannemora where the prison is located. The town is 170 miles north of the state capital of Albany, and on the edge of the Adirondack Park, featuring forests, mountains and lakes.

Roadblocks manned by heavily armed state troopers were set up on roads in the region. Canadian officials were also on the lookout for the escapees.

State police said they have investigated about 100 leads so far without finding the killers.

“It was an elaborate plot,” said Cuomo.