With flags, candles and glow sticks, thousands of people hugged, cried and prayed. At the end of the vigil, 19 balloons went up, one for each victim.
"It is our job to put the best, the brightest, the smartest, the most agile force between you and danger. We did that the other night," Prescott Fire Chief Don Devendorf said to the crowd as he broke down.
Also at the vigil was Brendan McDonough, the lone survivor of the elite firefighting crew. Officials on Tuesday said McDonough, 21, "did exactly what he was supposed to" on that fateful afternoon when 19 of his colleagues died while battling the Yarnell Fire.
McDonough was the only member of the Granite Mountain Hotshots to survive. Officials say he is extremely distraught over the loss of his colleagues. McDonough was serving as a lookout and was in charge of relaying key information to his team.
"He was on a hillside, within a mile or two of the crew, so that he's not only in radio contact, but visual contact," said Wade Ward, spokesman for the Prescott Fire Department.
Ward said McDonough notified the other Hotshots that the weather was changing rapidly and that the fire had switched direction. McDonough also told them that he was leaving the immediate area to get to a "safety zone."
Wade said the fire turned so quickly, even though McDonough warned his team to leave, they just couldn't get out in time. The 19 firefighters deployed their emergency shelters in a last ditch effort to survive, but it was too late.
Crews are trained to dig into the ground and cover themselves with the fire-resistant, tent-like cover in hopes that the flames will burn over them.
Fire officials say the crew was in an extremely difficult part of the mountain to try to fight fire.
"That area that's out on that hillside there is a very difficult fire to fight. It's a lot of mesquite, grasses. And when you look at, it seems so innocuous, because it's just very short, there's not a lot of large timber. But the vegetation out there, that mesquite is extremely oily. Once that starts, an ember gets into those extremely dry fuels, that fire is going to rip," said Karen Takai of the Southwest Incident Management Team.
An investigation into what exactly went wrong continues. Mary Rasmussen, a spokeswoman for the Southwest incident team, said Atlanta National Incident Management Organization (NIMO) will be the lead in the probe and will aim to put out a report in the coming days with preliminary information.
The 8,400-acre blaze was 8 percent contained, officials said Tuesday night. They expect to have full containment by July 12.
There are 18 engines, eight support water tenders and a total of 500 personnel battling flames. Temperatures were expected to be in the 90s in Prescott, with humidity at 15 percent and winds gusting up to 20 mph or higher in the event of a thunderstorm.
A lightning strike Friday in Yarnell, about 90 miles northwest of Phoenix, sparked the fire at a time of triple-digit heat and low humidity.
An estimated 200 homes are threatened and 50 have been destroyed. The Yarnell Fire Department and Yavapai County will continue to assess the community Tuesday. President Barack Obama has promised necessary federal support.
But if dealing with some of the most difficult fire conditions isn't enough, firefighters on the front lines are still dealing with incredible loss.
"It's really difficult to get a handle on and comprehend what's gone down here in the last few days. Every morning is spent No. 1, recognizing the sadness and the tragedy here, and then No. 2, trying to get yourself back into the work that needs to be done here on the ground," said Takai.
"Explosive fire behavior" likely trapped crew
Fire behavior described as "explosive" and unpredictable likely trapped and killed the firefighters, according to authorities.
Dry thunderstorms bringing strong, erratic winds that shifted unexpectedly in the high heat likely created the deadly conditions. Winds were notably unpredictable, contributing to rapid shifts in the flames.
The wildfire arrived at the onset of Arizona's monsoon season. The phenomenon brings lightning strikes, gusty winds, dust storms and sometimes rain to the state during the summer months.
The combination of the monsoon storms and erratic winds created a deadly situation.
"When those two collide, you get unexpected fire behavior and surprising fire behavior and explosive fire behavior," said Karen Takai, fire information officer at Sandia Ranger district in New Mexico.
Arizona has also been stricken by a severe drought, with 75 percent of the state affected.
ABC News and The Associated Press contributed to this report.