NEW YORK — (CNN) Convicted killer David Sweat escaped from his prison cell not once, not twice, but almost every night for several months, he told authorities, according to The New York Times.

And during those nightly jaunts, Sweat learned his way through the maze of tunnels and pipes in the bowels of the Clinton Correctional Facility — eventually devising the escape route that he and fellow inmate Richard Matt used to break out of the maximum security prison, he told investigators.

All the while, prison guards apparently had no idea what was happening. Sweat ventured out after the 11:30 p.m. head count, when he suspected guards were asleep, the Times reported. He crawled back into his cell each morning before the 5:30 a.m. check.

This continued for many nights until June 6, when guards made their morning rounds and discovered Sweat and Matt were gone.

Matt, who was imprisoned after killing and dismembering his boss, was already a veteran escapee. In 1986, he broke out of an Erie County jail where he was serving time for a previous crime.

But Sweat was the mastermind behind this escape, he told authorities from his hospital bed, where he was recovering from two gunshot wounds sustained during his capture.

Matt wasn’t there to defend or dispute the claim; he was shot and killed by police while on the run.

Sweat said the plot to break out actually started in January, Clinton County District Attorney Andrew Wylie has told CNN.

It was that month, the Times reported, that Matt and Sweat were moved into cells next to each other. Sweat used a hacksaw to cut a hole in his cell, then a hole in Matt’s cell.

How did Sweat get access to a hacksaw? Joyce Mitchell, a prison tailor who has been charged with aiding the escapees, has admitted to smuggling hacksaw blades by hiding them in frozen hamburger meat, a law enforcement official told CNN last month.

At one point, another inmate heard what sounded like someone using a saw and asked Matt about it, the Times reported. Matt, known in the prison as a skilled artist, told the inmate he was stretching out painting canvases.

Sweat’s nightly ventures into the hidden tunnels of the prison were marred by dead ends and obstacles, the Times said.

He found a sewer tunnel, which reminded him of the escape route used in the movie “The Shawshank Redemption,” Sweat reportedly told authorities. But the real-life sewer tunnel led to a dead end.

Then he found a portion of tunnel that led to outside the prison walls, according to Sweat’s account. He said he used a sledgehammer to try to break through the concrete tunnel wall, which eventually proved futile.

His lucky break came around May 4, the Times reported, when the prison shut down its heating system for the season. A 24-inch steam main that’s usually too hot to handle started to cool. That pipe traveled through the concrete wall that Sweat couldn’t break through.

Sweat started carving through the large pipe with hacksaw blades, according to his account. After more than four weeks, they had entrance and exit holes big enough for both men to crawl through.

The night before their escape, Sweat and Matt slipped out of their cells and made a practice run all the way to a manhole leading out of the tunnel. The following night, they escaped Clinton for good — only to discover their getaway driver never showed up, officials said.

Despite their botched getaway plan, Sweat and Matt managed to elude authorities for about three weeks. They fled through the woods of upstate New York, breaking into a vacation cabin and collecting supplies.

But eventually, Matt became a burden to the younger, more athletic fugitive.

“Sweat felt that Matt was slowing him down,” New York Gov. Andrew Cuomo said last month. Sweat also told investigators he was irked by Matt getting drunk from alcohol found in a cabin.

He eventually ditched Matt, who didn’t make it much farther. He died June 26 after getting shot by police.

Sweat came within two miles of the porous Canadian border before an officer found and shot him. He has been released from an Albany hospital and is now in solitary confinement at another prison.

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