That fact, revealed in an official investigative report on the fire released on Saturday, explains one of several unanswered questions surrounding the event, the deadliest day for American firefighters since the September 11, 2001, terrorist attacks, and perhaps the most vexing: why did the men end up where they did?

The report, the result of a three-month investigation by a panel of firefighting experts, did not assign blame for the tragedy and affirmed that the firefighters followed proper procedures. Still, it outlined several problems, such as radios that sometimes did not work properly, updates that did not give a precise sense of the crew's movements and the 33 minutes of radio silence.

"Nobody will ever know how the crew actually saw their situation, the options they considered or what motivated their actions," the report said.

The Granite Mountain Hotshots' sole survivor, Brendan McDonough, was working as a lookout that day and left his post on a separate ridgetop once he noticed the flames change direction in the distance. As he was leaving, the crew's captain, Jesse Steed, told him over the radio, "I've got good eyes on you and the fire, and it's making a good push."

Soon, the firefighters would be lumbering down the mountain, to a valley still untouched by the fire.

Investigators said they could offer only educated guesses to explain where the firefighters wound up. The crew left the village of Yarnell, where the fire started, and travelled parallel to the flames, building a fire break as a way to contain the blaze.

The firefighters travelled southeast near a ridge top, the report said, before descending towards a ranch in Yarnell, perhaps in an attempt to reposition themselves and get back to fighting the flames.

The report said the crew "did not perceive excessive risk". Winds from a thunderstorm that had been forecast to roll over the area hooked the flames and sent them straight towards the 19 firefighters during the 33 minutes in which there was no contact between them and the commanders.

The men died about 550 metres from their destination. Having hiked the same route the crew took that day, the investigators concluded that the ranch probably looked closer than it was. The area was covered with dried vegetation and big granite boulders, causing the men to travel at about half their regular speed, the report said.

As they descended from the ridge, they gradually lost sight of the fire. As they entered the basin at the base of the mountain, flames emerged ahead of them, leaving them no option to escape. A plane loaded with fire retardant was flying over the area at the time, but its pilot had no clear sense of where the men were.

Based on the speed the fire was moving – 16-19 km/h – investigators estimate that two minutes passed between when the firefighters spotted the approaching flames and when they deployed their emergency shelters.

The deployment site was "not survivable," the investigators said, because there was too much vegetation there, causing the flames to sweep over the men. They said the temperature of the fire climbed above 1000 degrees, well above the 650 degrees that the fire shelters were designed to withstand.

The wildfire began on June 28 and quickly grew into an inferno that destroyed more than 100 structures and burned 33 square kilometres before it was contained 12 days later. A crucial focus of the investigation was on the 33 minutes with no recorded radio communication between the crew and anyone else working the fire, allowing the men to shift locations without anyone else knowing where they were going or the command centre being able to steer them away from danger.

At a news conference on Saturday, Jim Karels, the Florida state forester who was in charge of the investigative team, said the team could not tell whether the firefighters could have been saved if there had been no lapse in contact.

Relatives of the dead firefighters were briefed on the report earlier in the day, before its release to the media and the public.

Juliann Ashcraft, whose husband Andrew died, said she walked away wondering what, if anything, would be done to prevent such a tragedy from happening again.

"Why didn't they have more technology on them, something to tell where they were, more eyes and ears?" she asked.

One of the report's recommendations was that the state consider equipping wilderness firefighters with GPS devices to help track their whereabouts.

The investigators said they were able to determine that as the flames closed in on the 19 men, none abandoned the tight formation or procedures they had practised so many times in drills – entering their shelters in order from the least to the most experienced, rookies at the centre, veterans on the edges. Seven of the men were found inside fully deployed shelters. Four were inside shelters that had been mostly deployed, and eight were in partially deployed shelters.

The investigators pored through radio transmissions, logs from safety briefings and statements from people involved in finding the group after its superintendent, Eric Marsh, delivered his last, ominous message: "The Granite Mountain Hotshots are deploying their fire shelters.

New York Times