Night after night for months, David Sweat slipped through a hole he had sawed at the back of his cell in the Clinton Correctional Facility in northern New York. He would plumb the catacomb-like tunnels beneath the prison, where he was serving a life sentence for murder, searching for an escape route, confident that the guards would have no idea he was gone because they were asleep. Then he would return to his empty bunk.

His explorations began this past winter and continued through the spring. They took him underground almost every night for hours until he finally stumbled on what would become, through trial and error and countless hours of grueling work, his subterranean route out.

Sweat felt free during his nightly journeys into the maze, as though he had already escaped the ugliness of his day-to-day prison life.

Sweat has revealed those details and more to investigators reviewing his stunning June 6 escape with another inmate from the maximum-security prison in Dannemora, New York, according to several people briefed on his account. He has gone into the planning and execution of his bid for freedom in extraordinarily specific terms, portraying himself as the driving force.

It is a story of patience, timing, determination and physical strength — borne perhaps of a life of incarceration — along with good luck, and a MacGyver-like sense of ingenuity. For example, when Sweat was trying to cut through a concrete wall and heat from steam pipes in the underground passage became unbearable, he rigged a fan taken from his cell using electricity from the tunnel’s lights.

But it is also a story of neglect by those who were supposed to keep Sweat behind bars; of rules and procedures ignored; and of a culture of complacency among some prison guards, employees and their supervisors, whose laziness and apparent inaction — and, in at least one instance, complicity — made the escape possible.

Sweat’s statements, one of the people briefed on the account said, have in large measure been either corroborated or otherwise found credible. They have provided the authorities with a treasure trove of information about how he and another convicted killer, Richard W. Matt, were able to escape.

Delivered from his hospital bed in matter-of-fact tones, at times with apparent relish over his accomplishment, Sweat’s account covered his search for an escape route, as well as the arduous and monotonous work of digging through walls and sawing through steam pipes, according to several of the people briefed on his statements.

Sweat told the investigators that the plan had long been in the works but his efforts began in earnest after he was transferred to a cell next to Matt’s in late January. Almost immediately, he began using a hacksaw blade during the night to cut a hole in the back of his cell, and then cut through the back of Matt’s cell, several of the people said.

An inmate asked about the noise, telling Matt that he heard something that sounded like sawing. Matt, a painter who had provided some of his works to at least one corrections officer in exchange for favors, told the inmate that he had been stretching canvas or working on a frame, Sweat told the investigators, according to one of the people briefed on his account.

By February, Sweat had access to the enclosed catwalks behind the cells, he told the investigators.

He would wait each night until after the 11:30 head count to crawl through the hole, shinny down a series of pipes going down several stories and begin roaming the tunnels. He would return to his cell each morning before the 5:30 a.m. count, camouflage his portal to the maze below and start his daily routine.

At one point he found what he thought would be his way out — a sewer pipe, which he noted was the escape route used in the 1994 film "The Shawshank Redemption," one of the people said. It turned out to be a dead end.

But he did not give up. Later, according to his account, Sweat found a spot in a tunnel that ran beneath the prison’s outer walls where a series of pipes passed through the tunnel wall. Sweat told the investigators that he could see, along the length of the pipes as they traveled through the wall, that they emerged on the other side in another tunnel, some 20 feet away, outside the prison’s walls.

Using a sledgehammer and some other pilfered hand tools, he began to chip away at the concrete of the tunnel wall. Because of the dust and grime, he took a second set of clothes into the tunnel to serve as work coveralls.

The wall was rock solid, however, and progress was maddeningly slow, according to his account. But he got lucky. Around May 4, when the prison shut down its heating system for the season, one of the pipes, a blistering 24-inch steam main, started to cool. So he opted for a shortcut and decided to cut into the large pipe, which traveled through the large concrete wall. Using hacksaw blades with handles fashioned from rags, it took him more than four weeks of methodical work to cut holes into and out of the pipe that were large enough for the men to crawl through.

Days later after they had completed work on the pipe, and after first conducting a dry run to check the route, he and Matt left Clinton for what they thought would be the last time, emerging from a manhole cover outside the prison wall in the summer darkness.

The pair apparently gave far less thought to what they would do once outside the prison. A civilian worker who was supposed to pick them up in a car, Joyce E. Mitchell, never showed up, and without an apparent Plan B, Sweat and Matt fled into the woods.

Hundreds of state troopers, corrections officers, federal agents and local officers scoured the rural areas around the prison and chased leads as far away as the southwestern corner of the state with reported sightings as far away as Philadelphia.

The two eventually split up. Matt was shot and killed by a federal agent on June 26 when he refused to drop a shotgun.

Two days later, a state police sergeant happened upon Sweat on a rural road a mile and a half from the Canadian border. He chased him into an open field, and when the prisoner refused his order to stop running, the sergeant, a firearms instructor, dropped to one knee and fired, striking him twice from a distance of more than 50 yards with a .45-caliber pistol, two people briefed on the shooting said.

Sweat provided the account to investigators from the State Police, the Corrections Department and the state Inspector General’s Office during several sessions in recent weeks, according to the people briefed on his statements. They spoke on the condition of anonymity because they were not authorized to talk about the investigation.

The escape, the manhunt and the resulting spectacle proved to be an embarrassment for the Corrections Department and the administration of Gov. Andrew M. Cuomo.

The investigation, and a review of the corrections agency’s policies and procedures at Clinton by the office of the state inspector general, Catherine Leahy Scott, is continuing. Sweat’s account, along with interviews of corrections officers and prison officials, documents and reviews of other evidence, will no doubt play a significant role in determining what went wrong at the prison and within the culture of the agency.

An initial investigation led to the arrest of Mitchell. The charges, brought by the Clinton County district attorney, Andrew M. Wylie, accused her of smuggling hacksaw blades, chisels and other tools into the prison.

The superintendent at Clinton, two senior members of his staff and nine correction officers were also placed on administrative leave, according to prison agency officials, who said the superintendent was expected to retire at the end of July.

Sweat is being held in solitary confinement at the maximum-security Five Points Correctional Facility in Romulus, New York, officials said. Formal disciplinary charges have been filed against him in the escape.

Like many who followed the prison break, Sweat and Matt could not help but compare their efforts to the escape in "The Shawshank Redemption." Indeed, Sweat told investigators that he and Matt had joked that while it had taken Andy Dufresne, the character in the movie played by Tim Robbins, 20 years to escape, it would take them only 10 years.

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