Details about the three weeks two escaped killers spent on the run in upstate New York have begun to emerge from the sole survivor, who disclosed to the cops who captured him the duo's plans to escape to Mexico and how they split up as more than 1,200 police and federal authorities bore down on them in the rugged wilderness near the Canadian border.

David Sweat, who remains in critical condition at Albany Medical Center, was shot twice in the torso Sunday after he ran from an officer near the small hamlet of Constable, told authorities about the days and weeks following the daring, June 6 escape he and Richard Matt pulled off from the Clinton Correctional Facility in Dannemora, N.Y., Gov. Andrew Cuomo said Monday. Matt got sick and was apparently ditched by his cohort as they made their way north, always planning to eventually make their way to Mexico, Cuomo said.

"Matt was slowing Sweat down."

- Gov. Andrew Cuomo

"Matt was slowing Sweat down," Cuomo told WCNY Monday, explaining that the 35-year-old fugitive left Matt some five days prior to Friday, when police caught up with Matt and shot and killed the 49-year old convicted murderer.

The pair's plan to escape to Mexico imploded when prison worker Joyce Mitchell, who was supposed to drive them 2,500 miles to what they hoped would be freedom south of the border got cold feet and was not waiting for them when they emerged from a manhole following their escape.

Cuomo was relating details Sweat apparently divulged after he was apprehended. Doctors were fighting Monday to keep Sweat alive, while investigators wait to interrogate him further.

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Sweat was captured alive, but badly injured around 3:20 p.m. Sunday, when State Police Sgt. Jay Cook spotted Sweat walking down a road in the town of Constable, about 1½ miles from the Canadian border. Sweat cut toward a line of trees and refused commands to stop, authorities said.

Fearing Sweat could make it to the tree line and disappear into the forest, Cook fired two shots and hit Sweat in the torso, New York State Police Superintendent Joseph D’Amico said.

“It was a very courageous act,” Cuomo said Sunday afternoon, which was filled with cheers from the audience.

A photo captured Sweat wearing a hooded parka and camouflage pants, with smears of blood on his face. As authorities carried him away to a hospital in Malone, he coughed up blood. When authorities interview Sweat, they could learn more details about how he and Matt pulled off the improbably escape, the first in the prison's 170-year history.

Matt was gunned down by authorities on Friday after he failed to drop a stolen gun he was carrying, according to law enforcement. Police had been hot on his trail after finding soiled underwear at a burglarized cabin Wednesday that belonged to Matt, DNA testing showed, the Buffalo News reported. A person towing a camper reported that he had heard a loud sound near the town of Malone and discovered a bullet hole in his trailer.

Police went to the scene where the tipster had heard what turned out to be a gunshot and found a nearby cabin, where there was evidence someone had recently fled. As they searched the area, a noise the likely result of Matt's condition gave him away.

"As we were doing the ground search in the area, there was movement detected by officers on the ground, what they believed to be coughs. So they knew that they were dealing with humans as opposed to wildlife," D'Amico said.

A border patrol agent spotted Matt in the brush, and ordered him to show his hands, D'Amico said. When Matt didn't comply, he was shot dead.

A 20-gauge shotgun, likely stolen from a hunting cabin, was found on Matt, authorities said.

An autopsy showed Matt had been shot three times in the head, state police said Sunday.

Matt's body also bore the signs of three weeks on the run in the inhospitable wilderness. He had bug bites on his legs, and bore blisters and minor abrasions that would be expected for someone who had been living in the woods. He also smelled of alcohol, according to the Buffalo News.

Authorities believe Matt was sick, possibly from consuming spoiled food or bad water, a law enforcement source told the newspaper.

Fox News' Laura Ingle, Rick Leventhal and The Associated Press contributed to this report.