Brendan McDonough was on lookout for the Granite Mountain Hotshots when he spotted a sudden, erratic shift in the weather that was to prove catastrophic for the rest of his crew.
The Hotshots, an elite US firefighting unit, were battling a forest fire near Yarnell, Arizona, and McDonough had been charged with relaying key information to the team.
From a hilltop more than a kilometre away from the fire, the 21-year-old radioed the 19 firefighters on the ground to warn them that the "weather was changing rapidly" and had reached a "trigger point".
The blaze was coming their way and they needed to get out. McDonough barely made it to safety, with the fire ripping through his lookout point less than three minutes after he left it. But two walls of flame overtook his friends, resulting in the US's biggest loss of firefighters since September 11, 2001.
Those killed were: Andrew Ashcraft, 29; Robert Caldwell, 23; Travis Carter, 31; Dustin Deford, 24; Christopher MacKenzie, 30; Eric Marsh, 43; Grant McKee, 21; Sean Misner, 26; Scott Norris, 28; Wade Parker, 22; John Percin, 24; Anthony Rose, 23; Jesse Steed, 36; Joe Thurston, 32; Travis Turbyfill, 27; William Warneke, 25; Clayton Whitted, 28; Kevin Woyjeck, 21; and Garret Zuppiger, 27.
Wade Ward, a spokesman for the Fire Department in Prescott, Arizona said the tragedy had traumatised McDonough. "He just watched his friends die."
He asked the media to respect his privacy and let him and the other families mourn.
"He's trying to deal with the same things that we're all trying to deal with, but you can understand how that's compounded being there on the scene," Ward said.
Juliann Ashcraft, who lost her husband Andrew Ashcraft in the fire, said she hoped McDonough "knows we love him".
"The first time I saw him after the fire, I gave him a big hug and he still smelled like the fire, the same way my husband would smell when he'd come home," she said.
In a statement, McDonough paid tribute to his "fallen brothers".
Investigators will be keen to talk to McDonough to work out how a forest fire many had believed was containable turned into an inescapable killer.
Ward said that McDonough was "doing exactly what he was supposed to do. He left his post based on protocol, and he was moving to a new position. He was doing his job and the hotshot crew was doing their job. This is why they call this kind of thing an accident".
BLACK SWAN THEORY
Cory Moser, division chief of the Prescott Fire Department, said the desolate scene where the 19 firefighters died was one clue that whatever killed them may well turn out to have been an unexpected "black swan" event - a rare turn of the weather, conditions or luck that no one expected or could have prevented.
"For them to have been run over like that tells me that something spectacular happened, something really unusual," he said.
Many fire professionals in the region are reluctant to speculate about what might have happened. But those who knew the Granite Mountain Hotshots, noting their superior physical conditioning and extensive training, and the ferocity of the blaze they were battling, said they believed the result may turn out to be, as some authorities have suggested, a sudden shift in the wind or something similar.
One of the few predictable things about wildfires, they said, is their unpredictability.
"The difference between a structure fire and wildland fire is that the wildland fire will come get you, as we found out in a terrible, terrible way the other day," said Don Devendorf, another division chief with the Prescott Fire Department.
Wildland fires, which in the high desert of Arizona inevitably mean steep terrain, dry conditions and terrible heat, force firefighters to gauge the winds, the weather, the condition of the brush fuelling the fire and even which way the hill faces. A south-facing hill absorbs more heat over time, Devendorf said.
"We can pretty much predict how something is going to behave inside four walls," Moser added. "When you're standing on the side of a mountain, sometimes weather just decides to do what it's going to do."
"It's kind of like driving a car," he said. "You can do everything right and it doesn't mean the person on the other side isn't going to cross the double yellow line and hit you. And it's the same with fires."
FIRE SERVICE'S 'NAVY SEALS'
The Hotshots of his department, whom Devendorf likened to the elite Navy SEALS, trained extensively to stay safe under such conditions.
They and other firefighters deployed lookouts to watch for sudden changes in the direction of the fire, maintained escape routes and safety zones and are assisted by meteorologists.
The Granite Mountain Hotshots, the only crew in the US that is part of a municipal fire department, also were in peak physical condition, able to run 16km in boots while wearing 19kg packs.
Fourteen of those killed were young men in their 20s who could handle the challenge of hiking in to a fire with chain saws and other equipment, although their leader, Eric Marsh, was keeping up at age 43.
And sometimes it just doesn't matter how prepared you are, firefighters said. Winds can shift in a matter of seconds and can't be outrun, Devendorf said. A column of smoke thousands of feet high can attract moisture and suddenly collapse, blasting its own winds in all directions. A developing storm 32km away can affect the scene of a fire.
"We're learning," said Devendorf, who met with some of the Hotshot crew members' families after the men were killed. "Unfortunately, we learn through bad events."